Impaired waters in Colorado.

Clean Water Act assessment is done by the states, on their own budgets. Roughly half the country's subwatersheds contain no assessed water at all, and a water nobody has tested is not a water known to be safe. Everything on this page is a share of what has been assessed, and the not-assessed share is shown next to it for exactly that reason.

A water is impaired when a designated use — swimming, fishing, drinking water supply, aquatic life — is not being supported. It sits on the 303(d) list only while it is still awaiting a cleanup plan, a TMDL. Once that plan is written the water comes off the list and is still impaired. So the listed figure is the regulatory backlog, and the impaired figure is the state of the water; they are not two views of one number.

Driftwise re-serves EPA's ATTAINS data from a copy we refresh; we do not make assessments, and states update theirs on multi-year cycles. For the authoritative record of any water in Colorado, use EPA's How's My Waterway or Colorado directly.

Every subwatershed in the country against the states’ own Clean Water Act assessments — what is impaired, what is still on the 303(d) list, what is causing it, and how much of the country nobody has assessed at all.

Open the impaired waters map →

Watershed Explorer

Click any point in the country and read what six federal datasets say about it — flow, drought, fire, flood forecast, satellite cyanobacteria screening and Clean Water Act impairment — each one labelled with what it is actually a fact about.

Wildfire & Smoke Map — Colorado

Official NIFC fire perimeters and incident points under NOAA’s HRRR-Smoke near-surface forecast, filterable by size, state, and containment.

Open the national wildfire and smoke map →

Streamflow Map — Colorado

Every reporting USGS stream gauge in the country, coloured by how today’s flow ranks against that gauge’s own record for this calendar day.

Open the national streamflow map →

U.S. Drought Map — Colorado

The U.S. Drought Monitor — the country’s official weekly drought assessment — drawn across five severity categories from D0 to D4.

Open the national U.S. drought map →

Flood Outlook Map — Colorado

NOAA’s river forecast centres call the next few days at every forecast gauge in the country, on the National Weather Service’s own flood categories — action, minor, moderate and major.

Open the national flood outlook map →

Cyanobacteria Bloom Map — Colorado

NASA and EPA’s satellites read a pigment index over roughly 2,300 U.S. lakes large enough to resolve at 300 m. A pre-screening indicator, not a health assessment, and never a substitute for your state’s advisory.

Open the national cyanobacteria bloom map →

Critical Habitat & Protected Waters Map — Colorado

Every river and stream the federal government has designated as ESA critical habitat, the listed species each unit is designated for, and who manages the protected land around it.

Open the national critical habitat map →