Portage Lake Southwest Basin; Mendon Township is a productive, nutrient-rich eutrophic lake in St. Joseph County, Michigan. Water quality is graded D based on 1 sampling years through 2023. Overall water quality is improving over recent sampling years. The lake supports 3 documented fish species including Chestnut lamprey, Common shiner, and Rainbow darter. Public access is available with 1 public boat landing. Compared to the 12 other monitored lakes in St. Joseph County, Portage Lake Southwest Basin; Mendon Township ranks #9 for water quality.
Source: EPA Water Quality Portal sampling records, Michigan DNR, last sampled 2023-09-10. Grade methodology: LakeGrade methodology.
Watch Portage Lake Southwest Basin; Mendon Township water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Murky, only visible to about 5 ft. Trophic State Index: 54.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5 ft | D |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 54 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Portage Lake Southwest Basin; Mendon Township
Compare lakeside cabins, hotels, and vacation rentals near Portage Lake Southwest Basin; Mendon Township in St. Joseph County, Michigan — 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 Portage Lake Southwest Basin; Mendon Township
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 trip to Portage Lake Southwest Basin; Mendon Township?
Get lake water-quality report cards plus the best cabin & lodging deals near Portage Lake Southwest Basin; Mendon Township — straight to your inbox. No spam, unsubscribe anytime.
Planning a whole trip? See where to stay at Michigan’s top lakes →
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Portage Lake Southwest Basin; Mendon Township
- → Portage Lake Southwest Basin; Mendon Township fishing forecast & best times (species outlook + 14-day solunar calendar)
- → Portage Lake Southwest Basin; Mendon Township fishing regulations (limits, seasons, special rules)
- → Is it safe to eat fish from Portage Lake Southwest Basin; Mendon Township? (mercury & PFAS guide)
Water Quality Trend: ↑ Improving
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +1.835 m/yr | 3 |
Recreation & Access
Water Temperature
Portage Lake Southwest Basin; Mendon Township averages about 64°F at the surface in summer, usually warmest in Jul (about 65°F) and coldest in May (about 58°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 277 field readings (2016–2019) via the EPA Water Quality Portal. See the full Portage Lake Southwest Basin; Mendon Township water temperature breakdown →
Location
County Ranking
Ranked #9 of 13 lakes in St. Joseph County
Cleaner Lakes Within 30 Miles
Portage Lake Southwest Basin; Mendon Township holds Grade D. 4 nearby lakes hold higher grades.
- AFishers Lake North Central Basin; Park TownshipSt. Joseph County · 4.5 mi · Two grade letters higher (D → A)
- BIndian Lake Central Basin; Brady TownshipKalamazoo County · 7.4 mi · Two grade letters higher (D → B)
- BBarton Lake West Basin; Schoolcraft TownshipKalamazoo County · 3.8 mi · Two grade letters higher (D → B)
- CTemplene Lake Central Basin; Sherman TownshipSt. Joseph County · 10.6 mi · Higher grade (D → C)
Nearby Lakes in St. Joseph County
Explore Portage Lake Southwest Basin; Mendon Township across LakeGrade
Fish species and top-graded lakes across Michigan
Fish species and best lakes in St. Joseph County
Species activity outlook by water temperature and season
Where to stay at Michigan's top lakes, each with its grade
High nutrients, frequent algae, reduced clarity
Michigan's cleanest and most-polluted lakes, ranked
More Michigan Lake Rankings
Other Grade D Lakes in Michigan
Eutrophic Lakes in Michigan
More records, surveys & data sources
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Portage Lake Southwest Basin; Mendon Township under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Th Plastics IncMendon · 4.4 mi away · NPDES MIG250278Recent violation
- Parkville Prairie FarmsThree Rivers · 1.6 mi away · NPDES MIG440036
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.
Data Sources
Water quality data from the EPA Water Quality Portal
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2023-09-10
Monitoring stations: 1