Silver Lake
McHenry County, IllinoisView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
↑ up from B at the last regrade
- Mesotrophic
- Impaired · Mercury
- #1 of 5 in the county
- Public access
- Limited data
Silver Lake in McHenry County, Illinois has a water quality grade of A (Excellent). Water clarity: 7 ft visibility. Phosphorus: 12.5 µg/L. Chlorophyll-a (algae): 4.9 µg/L.
- Clarity
- 7 ft
- Typical in September
- 68°F
- Type
- Mesotrophic
- Public access
- Yes
Stays via Stay22
Stays near Silver Lake
Compare lakeside cabins, hotels, and vacation rentals near Silver Lake in McHenry County, Illinois — 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 Silver Lake
Prices for Sep 11–13, 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 Illinois’s top lakes →
Watch Silver Lake’s letter
Email me if this lake’s grade moves. Grades stay free.
Or email
Silver Lake is a mesotrophic lake in McHenry County, Illinois. Water quality is graded A based on 2 sampling years through 2020. Limited fish-species data available. Public access is available. Compared to the 4 other monitored lakes in McHenry County, Silver Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2020-10-14. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLimited data
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The A is nutrients and algae, not a swimming clearance. Silver Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Water Quality Grade: A (Excellent)
Moderate clarity, visible to about 7 ft. Phosphorus 12.5 µg/L. Chlorophyll-a 4.9 µg/L. TSI 45. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 7 ft | Not graded |
| Phosphorus | 12.5 µg/L | Good |
| Chlorophyll-a (Algae) | 4.9 µg/L | Good |
| Trophic State Index (TSI) | 45 | Mesotrophic |
Moderate nutrients, good water quality
Water Temperature
Silver Lake typically sits around 68°F at the surface in September. Summer average is about 78°F. Usually warmest in Jul (about 81°F) and coldest in Oct (about 55°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 122 field readings (2010–2020) via the EPA Water Quality Portal. See the full Silver Lake water temperature breakdown →
Fishing Silver Lake
Reservoir Info (USACE NID)
Silver Lake is a man-made reservoir impounded by the Silver Lake Dam (completed 1929), built primarily for recreation on the TRIB FOX RIVER; earth-type dam, 23 ft tall and 170 ft long.
- Normal storage
- 364 ac-ft
- Max storage
- 580 ac-ft
- Hazard class
- Low
- Owner
- VILLAGE OF OAKWOOD HILLS
Source: USACE National Inventory of Dams, NID ID IL00584 · Operator website
EPA Impairment Status
Silver Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit IL_RTW · Official waterbody report · Matched by proximity (0.02 km)
Regulated Pollution Sources Nearby
6 EPA-permitted facilities operate within about 5 miles of Silver Lake under Clean Water Act (NPDES) discharge permits, including 3 classified by the EPA as major dischargers. 4 facilities have a reported Clean Water Act violation in the past three years.
- Crystal Lake Wwtp #3Crystal Lake · 2.9 mi away · NPDES IL0053457MajorRecent violation
- Cary Wwtp, Village OfCary · 2.9 mi away · NPDES IL0020516MajorRecent violation
- Fox River Grove WwtpFox River Grove · 3.8 mi away · NPDES IL0020583MajorRecent violation
- Mathews CompanyCrystal Lake · 4 mi away · NPDES IL0072851Recent violation
- Killarney Water SystemCary · 0.9 mi away · NPDES ILG640285
- Precision Twist Drill CorpCrystal Lake · 2.6 mi away · NPDES IL0074276
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.
County Ranking
Ranked #1 of 5 lakes in McHenry County
Nearby Lakes in McHenry County
Frequently asked questions about Silver Lake
Where is Silver Lake?
- Silver Lake is a lake in McHenry County, Illinois. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Silver Lake?
- Silver Lake in McHenry County, Illinois has a water quality grade of A (Excellent). Water clarity: 7 ft visibility. Phosphorus: 12.5 µg/L. Chlorophyll-a (algae): 4.9 µg/L.
Is Silver Lake safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Silver Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen). Check local advisories before you swim.
What is the water temperature of Silver Lake?
- Silver Lake typically sits around 68°F at the surface in September, from 122 EPA Water Quality Portal field readings (2010–2020). That is a typical value for the month, not a live reading.
Explore Silver Lake across LakeQuality
5.2 mi away · cable-pulled, no boat wake
Species activity outlook by water temperature and season
Top lakes and where to stay in the Chain O'Lakes area
Where to stay at Illinois's top lakes, each with its grade
Moderate nutrients, good water quality
Illinois's cleanest and most-polluted lakes, ranked
More Illinois Lake Rankings
Other Grade A Lakes in Illinois
Mesotrophic Lakes in Illinois
Where this data comes from
52 measurements from 3 monitoring stations, 2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX52 samples · 2020
Analytical methods
- MEASURED IN FIELD
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (3)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)