Is Decatur Lake Safe for Swimming?
Decatur Lake in Macon County, Illinois has a water quality grade of D (Nutrient-rich). Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum. Water clarity: 1.3 ft visibility. Phosphorus: 103 µg/L. Chlorophyll-a (algae): 25 µg/L. Always check local health department advisories before swimming.
Key Metrics
| Metric | Value |
|---|---|
| Overall Grade | D (Nutrient-rich) |
| Water Clarity (Secchi Depth) | 1.3 ft |
| Phosphorus | 103 μg/L |
| Chlorophyll-a (Algae) | 25 μg/L |
| Location | Macon County, Illinois |
How does Decatur Lake compare?
With an overall water quality grade of D, Decatur Lake matches or beats the Illinois state average of Grade D. It ranks #1 of 1 lakes in Macon County by water quality score.
Water clarity (Secchi depth) sits at 1.3 feet. That signals heavy algae or sediment, often tied to high phosphorus from runoff. Algae levels (chlorophyll-a) measure 25 µg/L — elevated; risk of harmful algal bloom advisories increases at this concentration.
Watch Decatur Lake water quality
Get an email when the grade, clarity, or algae reading changes. Unsubscribe anytime.