Rio Arriba County Lake Quality

Rio Arriba County's 24 monitored lakes fall in the moderate-density bracket for New Mexico. The county-level average smooths over real differences — a single agricultural watershed near the southwest corner can pull the average down even if the rest of the county runs clean. 4 of those lakes carry an A–F grade. The county-level summary describes that subset, not every water body listed. Rio Arriba County averages to a C. The distribution behind that average matters more than the letter: a few stressed lakes versus many decent ones can produce the same average as the inverse.

Most of the county's monitored lakes are shallow — under 50 feet — which means wind keeps the water column mixed all summer and sediment-bound phosphorus releases back into the surface layer whenever the bottom is disturbed. Abiquiu Reservoir Chama R Inlet (A) is the cleanest in the county.