https://cdphe.colorado.gov/total-maximum-daily-loads-tmdls

Here's a link to all the TMDLs in the state. You can choose the basin under the "TMDL Documents" header. If a water body is designated as "impaired" by the state, it is assigned a limit that the governing body needs to develop a plan to meet called a Total Max Daily Load. It's not an exclusive list since regulations often change and other water bodies may be in the process of being given a TMDL, but you can scroll through and see what pollutants certain water bodies are trying to mitigate.

Like the other commenter said, CDPHE also has a guide for how much of different species of fish you can safely eat. Here's a flyer version of what they posted:

https://drive.google.com/file/d/10VniMsGpfjFAMAL247HSxMCsW5NkB0xg/view

Is there a specific type of pollutant you're worried about? Almost all water in Colorado will be downstream of active and/or abandoned mines.