C-HAWQ, Coastal Habitat and Water Quality Initiative

Marco Island canal water quality

Free dock-water testing by C-HAWQ · {{RANGE_SHORT}}

C-HAWQ measured oxygen, temperature, and salinity from the surface to the canal floor at docks, bridges, and boat ramps across Marco Island. Each point on the map shows how healthy that water is for fish and marine life, and where oxygen runs low near the bottom. Select any point to see its readings.

Healthy oxygen — 5 mg/L or more at the bottom Some stress — 2 to 5 mg/L Low oxygen — below 2 mg/L Double ring — sampled on more than one date
One reading is a snapshot in time. Oxygen builds through the day as sunlight drives photosynthesis, so a site tested in the morning tends to read lower than the same site in the afternoon. Read each point as one moment, not a final grade. Sites with a double ring were sampled on more than one date — use the arrows in the readings panel (or swipe on a phone) to move between visits.
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Oxygen
Tide stage
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Step through one sampling day at a time
Bottom temperature (°F)
Minimum bottom temperature
Maximum bottom temperature
Bottom salinity (PSU)
Minimum bottom salinity
Maximum bottom salinity

Sampling locations

Marco Island canals
Selected sites

Site readings

Select a point on the map

How to read this

Fish and marine life need dissolved oxygen (DO) to breathe, measured in milligrams per liter (mg/L). Water above 5 mg/L is healthy; 2 to 5 puts fish under stress; below 2 is dangerous. Oxygen is usually lowest near the canal floor, so C-HAWQ profiles the full water column on every cast.

Select any numbered point to see its verdict, a surface-to-floor table, and depth charts for oxygen, saturation, temperature, and salinity.

What the data shows

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C-HAWQ has run {{NCASTS}} casts at docks, bridges, and boat ramps from {{DATE_FIRST}} to {{DATE_LAST}}. Most sites have been sampled once, so these readings show patterns worth watching, not final verdicts.

Water quality 101

What is dissolved oxygen?

Dissolved oxygen (DO) is the oxygen gas mixed into the water itself — the air that fish, crabs, and shrimp pull across their gills to breathe. It is measured in milligrams per liter (mg/L). When it runs low, animals that can't leave are stressed or suffocate, and a sharp drop is what drives a fish kill.

Two things set it. Sunlight lets seagrass and algae make oxygen during the day, so levels climb by afternoon and fall overnight. And warm, salty, still water near the canal floor holds less oxygen and mixes slowly — so the bottom is almost always the first place to run short. Healthy oxygen is a sign a canal trades water well with the bay.

What the numbers mean (mg/L)
5 and upHealthy — fish and seagrass thrive
2 to 5Some stress — sensitive species struggle
Below 2Low oxygen — most fish and crabs can't survive
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Casts, {{RANGE_SHORT}}
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Locations mapped
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Healthy at the floor
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In the low-oxygen range
Time of day

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Depth

The floor is where stress shows

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The range so far

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Bottom oxygen by time of day

Each point is one cast's bottom-water oxygen, plotted against the hour it was sampled. The upward slope is the time-of-day pattern; the scatter around it shows how much else is in play.

{{TREND_SRC}} Thresholds: UF/IFAS Extension FA-27; Florida DEP Rule 62-302.533, F.A.C. Exploratory — most sites sampled once.

How the canals stack up

Every mapped site's bottom-water oxygen on one scale. Dots are colored by health rating; the dashed lines mark the stress and low-oxygen thresholds.

Surface vs. bottom oxygen

Each dot is one site. Points below the dashed line have less oxygen at the floor than at the surface — the deeper water is where it thins.

Oxygen through the season

Bottom oxygen at every cast across the testing window. The navy line tracks the daily average.

Sites sampled more than once

Bottom oxygen (dots colored by rating)Surface oxygenShaded bands: green = healthy (5 mg/L and up), amber = some stress (2 to 5), red = low oxygen (below 2)

Swipe sideways to see more sites.

Repeat visits did not always happen at the same hour, and oxygen rises through daylight, so part of any change reflects the time of sampling. Hover over or tap a point to see when it was measured.