Where is Oswego Lake?

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

Oswego Lake

Kosciusko County, IndianaView map Directions

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

Clarity

9.9 ft

Clearer than most

Secchi · sampled 2024

Phosphorus

33 µg/L

Typical for Indiana

Measured by IDEM

Chlorophyll-a

2.2 µg/L

Less algae than most

Measured by IDEM

Type

Mesotrophic

Trophic class

Trend

Worsening

4 years of samples

Mesotrophic
Impaired · Impaired biota (cause unknown)

See the measurements Directions Where to stay

Oswego Lake in Kosciusko County, Indiana has water-quality measurements published by IDEM, shown here as reported. Water clarity: 9.9 ft visibility. Phosphorus: 33 µg/L. Chlorophyll-a (algae): 2.2 µg/L.

Loading map…

Free interactive depth-contour map of Oswego Lake, reaching a maximum surveyed depth of 40 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Indiana DNR.

Oswego Lake is a mesotrophic lake in Kosciusko County, Indiana. Overall water quality is declining over recent sampling years.

Source: EPA Water Quality Portal sampling records, IDEM, last sampled 2024-08-22. Methodology: how these readings are compared.

What Oswego Lake is good for

From access and monitoring records, not editorial picks.

Clear water9.9 ft of visibility

Swimming conditions

Readings only

Moderate algae

Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.

Nutrient and algae readings are not a swimming clearance. Oswego Lake is listed impaired under Clean Water Act §303(d) (IR 5) for impaired biota (cause unknown). Check local advisories before you swim.

Whether Oswego 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.

Compare swimming lakes near Fort Wayne →

Get alerts for Oswego Lake →

Water quality measurements for Oswego Lake

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

Good clarity, visible to about 9.9 ft. Phosphorus 33 µg/L. Chlorophyll-a 2.2 µg/L. TSI 44.

Water quality readings
Measure	Reading	Where it sits
Water clarity (Secchi depth)	9.9ft	Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer.
Total phosphorus	33µg/L	Fair GoodFairPoor
Chlorophyll-a (algae)	2.2µg/L	Good GoodFairPoor
Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a.	44	Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic

Moderate nutrients, good water quality

Ask about Oswego Lake

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

Stays via Stay22

Stays near Oswego Lake

Compare lakeside cabins, hotels, and vacation rentals near Oswego Lake in Kosciusko County, Indiana — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.

Top-rated places to stay near Oswego Lake

Prices for Oct 23–25, 4 adults. Change dates on the map below.

Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.

Planning a whole trip? See where to stay at Indiana’s top lakes →

Follow Oswego Lake’s readings

Email me when new measurements post for this lake. Updates stay free.

Or email

Fishing Oswego Lake

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

Water Quality Trend: Worsening

Based on 4 years of monitoring (2021–2024).

Water clarity
Worsening
4 years
Phosphorus
Worsening
+5.25 µg/L/yr4 years
Chlorophyll-a
Worsening
+0.2 µg/L/yr4 years

See year-by-year chart →

EPA Impairment Status

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

Causes of impairment

Impaired biota (cause unknown)

Designated uses not supporting: Aquatic life.

Source: EPA ATTAINS assessment unit INB06P1063_00 · Official waterbody report

Regulated Pollution Sources Nearby

6 EPA-permitted facilities operate within about 5 miles of Oswego Lake under Clean Water Act (NPDES) discharge permits.

Indiana University Foundation
Leesburg · 0.1 mi away · NPDES INRA02846
B & J Auto Salvage Inc
Leesburg · 1.9 mi away · NPDES INRM01333
Leesburg Municipal Stp
Leesburg · 3.3 mi away · NPDES IN0040258
Worthington Agriculture Parts
Leesburg · 3.5 mi away · NPDES INRM01600
Leesburg Dollar General
Leesburg · 3.5 mi away · NPDES INR10K096
Wwc Parking Expansion 2013
Warsaw · 4.2 mi away · NPDES INR10H135

Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.

Nearby Lakes in Kosciusko County

Stanton Lake—View →Tippecanoe Lake8.5 ft clear · Mesotrophic1.2 miView →Big Chapman Lake6.9 ft clear · Mesotrophic2.8 miView →Shoe Lake—View →Dewart Lake10.2 ft clear3.1 miView →James Lake5.3 ft clear · Mesotrophic3.1 miView →

Frequently asked questions about Oswego Lake

Where is Oswego Lake?: Oswego Lake is a lake in Kosciusko County, Indiana. Its water-quality measurements are published by IDEM and shown on this page as reported.
What is the water quality of Oswego Lake?: Oswego Lake in Kosciusko County, Indiana has water-quality measurements published by IDEM, shown here as reported. Water clarity: 9.9 ft visibility. Phosphorus: 33 µg/L. Chlorophyll-a (algae): 2.2 µg/L.
Is Oswego Lake safe to swim in?: Nutrient and algae readings are not a swimming clearance. Oswego Lake is listed impaired under Clean Water Act §303(d) (IR 5) for impaired biota (cause unknown). Check local advisories before you swim.

Explore Oswego Lake across LakeQuality

Lake Fishing Forecast

Species activity outlook by water temperature and season

Northern Indiana Lake Country

Top lakes and where to stay in the Northern Indiana Lake Country area

Indiana Lake Trips

Where to stay at Indiana's top lakes, each with its readings

The State of Indiana's Lakes

Indiana's cleanest lakes, ranked on agency measurements

More lakes in Indiana

All Indiana lakes

Every Indiana lake with its IDEM measurements

Lake water quality by country

Official ratings and named-lake measurements

Other Lakes in Indiana

Sparta Lake

Noble County · Measured

Goose Lake

Whitley County · Measured

Shriner Lake

Whitley County · Measured

Cedar Lake

Whitley County · Measured

Oliver Lake

LaGrange County · Measured

Olin Lake

LaGrange County · Measured

Mesotrophic Lakes in Indiana

Sparta Lake Goose Lake Shriner Lake Cedar Lake

Where this data comes from

11 measurements from 1 monitoring station, 2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.

Collected and reported by

North American Lake Management SocietyNALMS11 samples · 2021

Monitoring station identifiers (1)

EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.