Snohomish County Lake Quality

Snohomish County in Washington carries 52 monitored lakes — one of the lake-richer counties in our dataset. Coverage that dense usually reflects active lake-association sampling alongside state-agency monitoring. 1 of those lake carry an A–F grade. The county-level summary describes that subset, not every water body listed. Snohomish 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. Weallup Lake (C) is the cleanest in the county.