Greyrocks Reservoir
Platte County, WyomingView mapDirections
Clarity, phosphorus, and algae sit in the clean band for this region.
↑ up from C at the last regrade
- Eutrophic
- #3 of 9 in the county
- 78 ft max depth
- Public access
- Limited data
Greyrocks Reservoir in Platte County, Wyoming has a water quality grade of B (Good). Water clarity: 5.4 ft visibility. Phosphorus: 20 µg/L.
- Clarity
- 5.4 ft
- Max depth
- ~78 ft est.
- Type
- Eutrophic
- Phosphorus
- 20 µg/L
- Public access
- Yes
Stays via Stay22
Stays near Greyrocks Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Greyrocks Reservoir in Platte County, Wyoming — 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 Greyrocks Reservoir
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 trip? Cabins and lodging at Greyrocks Reservoir → · more Wyoming lake trips
Watch Greyrocks Reservoir’s letter
Email me if this lake’s grade moves. Grades stay free.
Or email
Greyrocks Reservoir is a productive, nutrient-rich eutrophic lake in Platte County, Wyoming with an estimated average depth of about 78 feet. Water quality is graded B based on 1 sampling years through 2018. Limited fish-species data available. Public access is available with 3 public boat landings. Compared to the 8 other monitored lakes in Platte County, Greyrocks Reservoir ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Wyoming DEQ, last sampled 2018-09-05. Grade methodology: LakeQuality methodology.
What Greyrocks Reservoir is good for
From access and monitoring records, not editorial picks.
- Boat launch3 documented ramps
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 B is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: B (Good)
Murky, only visible to about 5.4 ft. Phosphorus 20 µg/L. TSI 50. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.4 ft | Not graded |
| Phosphorus | 20 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 50 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~78 ft est. |
| Average Depth | ~58 ft est. |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Wyoming has not published bathymetry for Greyrocks Reservoir.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Recreation & Access
- Grayrocks Reservoir - EastPublic
- Grayrocks Reservoir - CentralPublic
- Grayrocks Reservoir - WestPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Greyrocks Reservoir
County Ranking
Ranked #3 of 9 lakes in Platte County
Nearby Lakes in Platte County
Frequently asked questions about Greyrocks Reservoir
Where is Greyrocks Reservoir?
- Greyrocks Reservoir is a lake in Platte County, Wyoming. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Greyrocks Reservoir?
- Greyrocks Reservoir in Platte County, Wyoming has a water quality grade of B (Good). Water clarity: 5.4 ft visibility. Phosphorus: 20 µg/L.
Is Greyrocks Reservoir safe to swim in?
- The B is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
How deep is Greyrocks Reservoir?
- No published bathymetric survey covers Greyrocks Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 78 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Are there boat ramps on Greyrocks Reservoir?
- Greyrocks Reservoir has 3 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Grayrocks Reservoir - East, Grayrocks Reservoir - Central, Grayrocks Reservoir - West. Public access is listed as yes.
Explore Greyrocks Reservoir across LakeQuality
7.4 mi away · recorded at 70°F
Species activity outlook by water temperature and season
Where to stay at Wyoming's top lakes, each with its grade
High nutrients, frequent algae, reduced clarity
Wyoming's cleanest and most-polluted lakes, ranked
More Wyoming Lake Rankings
Other Grade B Lakes in Wyoming
Eutrophic Lakes in Wyoming
Where this data comes from
24 measurements from 2 monitoring stations, 2015–2018. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- State of Wyoming Department of Environmental Quality Watershed Program
WYDEQ_WATERSHED24 samples · 2015–2018
Analytical methods
- Secchi
- Total Phosphorus After Block Digestion
Monitoring station identifiers (2)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory