Where is Riddles Lake?

Riddles Lake is a lake in St. Joseph County, Indiana. Its water-quality measurements are published by IDEM and shown on this page as reported.

How deep is Riddles Lake?

Riddles Lake has a maximum depth of 20 feet and an average depth of 7.9 feet. The lake covers 78 acres.

Riddles Lake

St. Joseph County, Indiana78 acresView map Directions

IDEM publishes the water-quality measurements for Riddles Lake. Here is what has been measured.

Phosphorus

133.8 µg/L

More phosphorus than most

Measured by IDEM

Chlorophyll-a

92.3 µg/L

More algae than most

Measured by IDEM

Max depth

20 ft

Bathymetric survey

Area

78 acres

Surface area

Shoreline

2 mi

Measured length

Impaired · Nutrients (phosphorus, nitrogen)
20 ft max depth
Limited data

See the measurements Directions Where to stay

Riddles Lake in St. Joseph County, Indiana has water-quality measurements published by IDEM, shown here as reported. Phosphorus: 133.8 µg/L. Chlorophyll-a (algae): 92.3 µg/L. Maximum depth: 20 ft. Surface area: 78 acres.

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Riddles Lake is a 78-acre lake in St. Joseph County, Indiana with a maximum depth of 20 feet (8-foot average).

Source: EPA Water Quality Portal sampling records, IDEM, last sampled 2021-07-14. Methodology: how these readings are compared.

Swimming conditions

No reading

Recreation use not supported

Nutrient and algae readings are not a swimming clearance. Riddles Lake is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.

Whether Riddles Lake is safe to swim in today is a call for the Indiana Department of Environmental Management and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.

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Water quality measurements for Riddles Lake

These are the measurements IDEM publishes for Riddles Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.

No clarity data. Phosphorus 133.8 µg/L. Chlorophyll-a 92.3 µg/L.

Water quality readings
Measure	Reading	Where it sits
Water clarity (Secchi depth)		No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer.
Total phosphorus	134µg/L	Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential.
Chlorophyll-a (algae)	92.3µg/L	Measured, not scored The green pigment in algae — a direct measure of how much algae is in the water.

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Answers come straight from the public measurements and survey records on this page.

Lake Details

Max depth

20 ft

Average depth

7.9 ft

Surface area

78 acres

Shoreline

2 mi

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Stays near Riddles Lake

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Fishing Riddles Lake

→ Riddles Lake fishing regulations (limits, seasons, special rules)

EPA Impairment Status

Riddles Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).

Causes of impairment

Nutrients (phosphorus, nitrogen)

Designated uses not supporting: Recreation.

Source: EPA ATTAINS assessment unit INK01P1069_00 · Official waterbody report

Nearby Lakes in St. Joseph County

Pleasant Lake1.1 miView →Sousley Lake9.5 miView →Chamberlain Lake11.7 miView →Saint Josephs Lake—View →South Chain Lake—View →Pinhook Lake—View →

Frequently asked questions about Riddles Lake

Where is Riddles Lake?: Riddles Lake is a lake in St. Joseph County, Indiana. Its water-quality measurements are published by IDEM and shown on this page as reported.
What is the water quality of Riddles Lake?: Riddles Lake in St. Joseph County, Indiana has water-quality measurements published by IDEM, shown here as reported. Phosphorus: 133.8 µg/L. Chlorophyll-a (algae): 92.3 µg/L. Maximum depth: 20 ft. Surface area: 78 acres.
Is Riddles Lake safe to swim in?: Nutrient and algae readings are not a swimming clearance. Riddles Lake is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
How deep is Riddles Lake?: Riddles Lake has a maximum depth of 20 feet and an average depth of 7.9 feet. The lake covers 78 acres.