Marin County Lake Quality

Marin County holds 12 monitored lakes. With a sample that small the county-level summary describes those specific waters, not necessarily every water body in the county. 1 of those lake carry recent nutrient and algae readings. The county-level summary describes that subset, not every water body listed. Phosphorus and algae readings vary widely across Marin County; the per-lake pages below carry the numbers.

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. Nicasio Reservoir has the lowest nutrient and algae readings in the county.