Question 1

Cleanest Lakes in St. Louis County, Missouri?

Accepted Answer

Simpson Park Lake in St. Louis County leads the rankings on measured clarity and nutrients and 1.9 ft of clarity. Below are the top 4 cleanest monitored lakes in St. Louis County, Missouri, ranked on EPA nutrient and algae measurements.

Question 2

What is the cleanest lake in St. Louis County, Missouri?

Accepted Answer

Simpson Park Lake in St. Louis County has the cleanest nutrient and algae readings in St. Louis County, Missouri, with 1.9 feet of measured water clarity.

Question 3

How are these rankings calculated?

Accepted Answer

Nutrients and algae, total phosphorus, nitrogen, chlorophyll-a and turbidity, are read against EPA National Lakes Assessment 2022 condition classes for that lake’s ecoregion. Water clarity (Secchi depth) is measured and shown separately. Lakes without enough recent samples are listed without a condition class rather than ranked low. Source data comes from the EPA Water Quality Portal.

#	Lake	County	Clarity	Phosphorus	Algae
1	Simpson Park Lake	St. Louis	1.9 ft	72.3 µg/L	23.8 µg/L
2	Mallard Lake	St. Louis	1.9 ft	84 µg/L	32.2 µg/L
3	Creve Coeur Lake	St. Louis	1.6 ft	101 µg/L	35.4 µg/L
4	Spanish Lake	St. Louis	1.6 ft	347.8 µg/L	62.6 µg/L

Cleanest Lakes in St. Louis County, Missouri

Ranked List

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