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How green the water is, merged from several satellites into one daily picture. The most complete colour layer we carry — but the cloud holes are filled in by estimate, not observed.

The sharpest daily colour composite, from the Sentinel-3 satellites. It only exists within about 108 nm of a coast, so blank open water is by design, and cloud holes are left empty.

How green the water is, straight from NASA's PACE satellite and on the map the same afternoon — about two days ahead of the other colour layers. Cloudy areas are left blank.

The freshest and sharpest colour picture we have — a single Sentinel-3 pass, on the map within about two hours. One pass only, so expect gaps, and cloud is left blank rather than filled.

How fast the surface current runs, from the satellite-measured slope of the sea surface. No wind push and no tide, so it reads smoother and slower than the forecast current layer.

How fast the surface current runs, worked out from satellite sea height plus the push of the wind. A daily average with no tide in it, and less reliable close to the coast.

How high or low the sea surface stands against its long-term average, measured by satellite — bulges are warm eddies, dips are cold. Each day is re-published over six days, so values can shift.

The height of the sea surface itself, measured by satellite — not a departure from average. Use it to see where a current edge actually sits, including over permanent features an anomaly map washes out.

How salty the surface is, blended from satellites, floats and ships into a complete daily map with no gaps. It runs six to seven days behind — our slowest layer — so read it for big fronts, not today's plume.

How salty the surface is, measured once a day by SMAP, a NASA satellite that reads moisture and salt from orbit. Where it did not pass the map is blank, not guessed. Two to three days behind.

The freshest map we have — rebuilt about every five minutes from GOES-19, the weather satellite over the Americas, as fast as it publishes. Each spot shows its newest cloud-free look from the last two hours, so it is nearly complete, but a patch under cloud can be two hours old.

One single scan from GOES-19, the weather satellite over the Americas, about every five minutes as it publishes. Every pixel is measured at the same instant with nothing filled in — expect a lot of cloud, and use the 2hr Composite for a fuller picture.

A daily map blended from four polar-orbiting satellites at 2 km. It is a night-time picture normalised to 1:30 am rather than this afternoon's water, and cloud holes are left blank.

Where NOAA's detector found a temperature break in yesterday's daily satellite picture. A yes-or-no mask, so most of the map is empty on purpose and blank means no satellite could see that water.

Where NOAA's detector found a temperature break in the hourly GOES-19 picture — the freshest break map we carry. Most of the map is empty by design; blank means cloud blocked the view.

Hourly temperature from GOES-19, the weather satellite over the Americas. “L2” is NOAA's raw operational file with no stitching — it reaches you sooner than L3, and looks rougher. Cloud stays blank.

Hourly temperature from GOES-19, the weather satellite parked over the Americas. “L3” means NOAA has stitched several passes onto a clean grid — tidier than the raw L2 feed, about an hour later.

NASA's daily satellite temperature map, and the sharpest observed layer we carry. NASA fills the cloud holes, so under heavy overcast you are reading an estimate rather than a fresh measurement.

How fast light dies out going down through the water — low is clear blue, high is murky. Calculated from satellite plankton readings, so it sees green water but not mud or river silt.

Roughly how deep you could still see a white disc lowered over the side — high is clear, low is murky. Same satellite source as Kd490, so it sees green water but not mud or silt.

A computer model's estimate of how much plankton is in the water. A simulation rather than a satellite picture, so it never has cloud holes and will not match the satellite chlorophyll layers.

A computer model's estimate of how much oxygen is in the water at the depth you pick. Low oxygen limits how deep a billfish or bigeye can comfortably hunt.

A computer model's estimate of living plant plankton, measured as carbon. A simulation with no cloud holes — and not the same thing as chlorophyll, even though the two look alike.

HYCOM's forecast salinity at a depth you pick, surface down to 656 feet. Read it alongside temperature to see where different bodies of water meet.

HYCOM's forecast of how salty the surface water is. Use it to find the edge where fresh river water meets blue — it is a simulation, not a measurement.

HYCOM's forecast of surface temperature, up to a week out. A simulation rather than a satellite picture, so there are no cloud gaps and it will not match your gauge — read the pattern.

The forecast height of the sea surface — warm eddies stand up as hills, cold ones sit in bowls, packed contours mean current. It includes the tide, so it will not match the satellite height layers.

HYCOM's forecast temperature at a depth you pick, surface down to 1312 feet. Step the depth slider to find where the colour changes fastest — that is the thermocline.

How fast the surface water moves, shown only where it spins the warm-core way — the rim of a warm-core eddy, where it rips fastest. Everywhere else reads zero.

Thin lines where the detector found a chlorophyll change sharp enough to call a front. A pixel is either on a line or not, so on a flat day the map is meant to come up empty.

Where modelled chlorophyll changes fastest across the map — the colour breaks, not the values. Brighter is a sharper change within that day's picture, so use it to find the line, not to measure it.

How fast the forecast surface water is moving — bright is fast, dark is slow. Speed only, not direction; for direction use Current Particles.

How fast the forecast water is moving at a depth you choose — 0, 82, 164, 328, 492 or 656 feet. Speed only; for direction use the Current Particles animation.

How fast the surface water moves, shown only where it spins the cold-core way — the rim of a cold-core eddy, where it rips fastest. Everywhere else reads zero.

Where the forecast sea surface bends most sharply, which is what the middle of an eddy looks like. Despite the name it is not a probability — it ranks within each day's picture, so treat it as context.

The lines where drifting things collect, traced by running particles back through 45 days of measured satellite current. Past days only — there is no forecast in this one.

The lines where drifting things collect — weed, foam, bait — traced by running particles back through 7 days of forecast current. Blank means it could not be worked out there, not that nothing is happening.

Whether the forecast current is pushing water up the slope toward shallower ground (red) or pulling it offshore (blue). Switched off over flat bottom, so a blank deep basin is normal.

Thin lines where the detector found a phytoplankton change sharp enough to call a front. A pixel is either on a line or not, so on a flat day the map is meant to come up empty.

Where modelled phytoplankton carbon changes fastest across the map — the edges, not the values. Brighter is a sharper change within that day's picture, so use it to find the line, not to measure it.

How slack the forecast surface water is — bright means slow enough that drifting things tend to stay put. Use it to find where weed and bait are likely to hold.

Thin lines where the detector found a salinity change sharp enough to call a front. A pixel is either on a line or not, so on a flat day the map is meant to come up empty.

Where the forecast salinity changes fastest across the map — the edges and rips, not the values. Brighter is a sharper change within that day's picture, so use it to find the line, not to measure it.

Where the forecast sea surface stands higher or lower than its long-term average. Red is a bulge, a warm-core clockwise feature; blue is a dip, a cold-core counter-clockwise one.

Thin lines where the detector found a temperature change sharp enough to call a front. A pixel is either on a line or not, so on a flat day the map is meant to come up empty.

Where the forecast temperature changes fastest across the map — the edges and rips, not the values. Brighter is a sharper change within that day's picture, so use it to find the line, not to measure it.

Where forecast surface water is squeezing together (red) or spreading apart (blue). Squeezing is where weed, foam and bait collect — and a mostly white map on a quiet day is normal.

The depth where forecast temperature changes fastest going down — the top of the cold water, in feet. It always returns a number, even where the water is barely layered.

In development: Atlantic Bluefin Tuna shades the water that is most like the water where bluefin have been caught, based on temperature, breaks, currents and depth. Its score is a 0 to 100 habitat match. Only a score of 50 and above is painted.

In development: the daytime bigeye map, built around bigeye dropping deep after sunrise; after dark, use Bigeye Tuna - Night. Its score is a 0 to 100 habitat match. Only a score of 50 and above is painted.

In development: the after-dark bigeye map, built around bigeye rising into shallower water at night; in daylight, use Bigeye Tuna - Day. Its score is a 0 to 100 habitat match. Only a score of 50 and above is painted.

In development: Blackfin Tuna shades the water that is most like the water where blackfin have been caught, based on temperature, breaks, currents and depth. Its score is a 0 to 100 habitat match. Only a score of 50 and above is painted.

In development: the daytime blue marlin map for the Gulf of America and the East Coast: its score is a 0 to 100 habitat match, using the thermocline and oxygen for daytime dives. Only a score of 50 and above is painted.

In development: the after-dark blue marlin map for the Gulf of America and the East Coast: its score is a 0 to 100 habitat match, using surface temperature because blue marlin stay shallow at night. Only a score of 50 and above is painted.

In development: the daytime blue marlin map for Baja: its score is a 0 to 100 habitat match, using the thermocline and oxygen for daytime dives. Only a score of 50 and above is painted. The Gulf of America and the East Coast get the Atlantic maps.

In development: the after-dark blue marlin map for Baja: its score is a 0 to 100 habitat match, using surface temperature because blue marlin stay shallow at night. Only a score of 50 and above is painted. The Gulf of America and the East Coast get the Atlantic maps.

In development: Cobia shades the water that is most like the water where cobia have been caught, based on temperature, breaks and depth. Its score is a 0 to 100 habitat match. Only a score of 50 and above is painted.

In development: King Mackerel shades the water that is most like the water where kings have been caught, based on temperature, breaks, currents and depth. Its score is a 0 to 100 habitat match. Only a score of 50 and above is painted.

In development: the daytime mahi map shades the water that is most like the water where mahi have been caught, based on temperature, breaks, currents and depth. Its score is a 0 to 100 habitat match. Weed lines and floating debris are not in it, and only a score of 50 and above is painted.

In development: the after-dark mahi map shades the water that is most like the water where mahi have been caught, based on temperature, breaks, currents and depth. Its score is a 0 to 100 habitat match. Weed lines and floating debris are not in it, and only a score of 50 and above is painted.

In development: Sailfish shades the water that is most like the water where sailfish have been caught, based on temperature, breaks, currents and depth. Its score is a 0 to 100 habitat match.

In development: Skipjack Tuna shades the water that is most like the water where skipjack have been caught, based on temperature, breaks, currents and depth. Its score is a 0 to 100 habitat match. Only a score of 50 and above is painted.

In development: the daylight swordfish map, built around swordfish holding deep after sunrise; after dark, use Swordfish - Night. Its score is a 0 to 100 habitat match. Only a score of 50 and above is painted.

In development: the after-dark swordfish map, built around swordfish rising into shallower water at night; in daylight, use Swordfish - Day. Its score is a 0 to 100 habitat match. Only a score of 50 and above is painted.

In development: Wahoo shades the water that is most like the water where wahoo have been caught, based on temperature, breaks, currents and depth. Its score is a 0 to 100 habitat match. Only a score of 50 and above is painted.

In development: White Marlin shades the water that is most like the water where white marlin have been caught, based on temperature, breaks, currents and depth. Its score is a 0 to 100 habitat match.

In development: Yellowfin Tuna shades the water that is most like the water where yellowfin have been caught, based on temperature, breaks, currents and depth. Its score is a 0 to 100 habitat match. Only a score of 50 and above is painted.

Contour lines through the hills and valleys of the forecast sea surface. Tight lines mean a steep slope and stronger current; the thick line is the zero level where high meets low.

The basemap is the picture under everything else: satellite imagery, coastline and place names from Mapbox. Pick one of nine looks in Preferences. It is not a nautical chart, and open water looks empty in the satellite views.

Draws measured satellite current as moving particles over whatever layer you have up — which way the water sets and roughly how hard. In forecast mode it follows the forecast current instead. No speed scale, and it turns off each time you open the app.

The Currents button draws moving arrows or streaks that show which way the water is moving and roughly how hard. They look a little different on a phone and on a laptop.

Bottom contour lines at nineteen fishing depths from 30 to 12,000 feet, each labelled. On the browser the numbers are always feet; the phone apps follow your depth-unit setting.

On the iPhone app a small crosshair sits fixed a little above the middle of the screen. Drag the map under it, and the readings along the top of the screen come from that exact spot. On the website the readings follow your pointer.

Tap the ruler button on the right and two pins appear with a line between them. Drag either pin and the distance updates. It gives the straight-line distance only, in your chosen units.

The boat icon marks where you are, drawn above every data layer, and its bow points where your phone is pointing, not your course. Tap the boat button on the right to recenter the map on yourself. If no icon appears at all, the app has no location permission.

Direction arrows from measured satellite current. Direction only and no speed — use a current speed layer for that.

Sea-surface-height contour lines from satellite rather than forecast — one snapshot a day, about a day behind. Tight lines mean a steeper slope and a stronger current.

The bar in the bottom-right corner of the map on the website shows what distance a length on screen represents, always in nautical miles. It is a rule of thumb. For an exact distance, use the ruler tool.

On the website, click the map with a species selected and a breakdown panel opens for that spot. The small white crosshair marks the exact point the panel describes and goes away when you close the panel. On the iPhone app the fixed map crosshair does this job.

The shaded picture of the bottom that sits under every other layer — shelf, canyons, ridges and the deep basin. Always on, with no controls of its own.

When you replay a finished trip from the Logbook, a boat icon sits on your track where you were at the moment the time slider points to. Drag the slider and the boat moves along the line. It never shows while recording or on the main map.

Fish-shaped marks that show where you caught fish on a recorded trip, colored by species with the name beside each one. They appear in the Logbook as you log catches on a live trip and whenever you open that trip afterward, never on the main map by themselves.

The line showing where you went on a recorded trip. It appears in the Logbook, live while you record and finished when you open a past trip, never on the main map by itself. A finished trip is colored by speed: yellow at 10 knots and under (trolling), red above (running).

Every waypoint we carry — rigs, artificial reefs, wrecks, wellheads and banks — across the Gulf, the East Coast and Baja.