Greyrocks Reservoir
Platte County, WyomingView mapDirections
Wyoming DEQ publishes the water-quality measurements for Greyrocks Reservoir. Here is what has been measured.
- Eutrophic
- 78 ft max depth
- Public access
- Limited data
Greyrocks Reservoir in Platte County, Wyoming has water-quality measurements published by Wyoming DEQ, shown here as reported. Water clarity: 5.4 ft visibility. Phosphorus: 20 µg/L.
Greyrocks Reservoir is a productive, nutrient-rich eutrophic lake in Platte County, Wyoming with an estimated average depth of about 78 feet. 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. Methodology: how these readings are compared.
What Greyrocks Reservoir is good for
From access and monitoring records, not editorial picks.
- Boat launch3 documented ramps
Swimming conditions
Readings onlyLimited data
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. Check local advisories before you swim.
Whether Greyrocks Reservoir is safe to swim in today is a call for the Wyoming Department of Environmental Quality and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Greyrocks Reservoir
These are the measurements Wyoming DEQ publishes for Greyrocks Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 5.4 ft. Phosphorus 20 µg/L. TSI 50.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 5.4ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 20µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 50 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Greyrocks Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
~78 ft est.
Public access
Yes
Listed by Wyoming DEQ
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
Watershed (drainage) area
4,192 sq mi
HydroLAKES / HydroSHEDS
Surface area
3,346 acres
HydroLAKES / HydroSHEDS
Shoreline
18.5 mi
HydroLAKES / HydroSHEDS
Elevation
4,403 ft
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
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Stays near Greyrocks Reservoir
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Fishing Greyrocks Reservoir
Nearby Lakes in Platte County
Frequently asked questions about Greyrocks Reservoir
Where is Greyrocks Reservoir?
- Greyrocks Reservoir is a lake in Platte County, Wyoming. Its water-quality measurements are published by Wyoming DEQ and shown on this page as reported.
What is the water quality of Greyrocks Reservoir?
- Greyrocks Reservoir in Platte County, Wyoming has water-quality measurements published by Wyoming DEQ, shown here as reported. Water clarity: 5.4 ft visibility. Phosphorus: 20 µg/L.
Is Greyrocks Reservoir safe to swim in?
- Nutrient and algae readings are 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.
Can I fish at Greyrocks Reservoir?
- Greyrocks Reservoir has 3 documented boat landings in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Wyoming's fish and wildlife agency, so check its current regulations before you go.
Explore Greyrocks Reservoir across LakeQuality
7.4 mi away · recorded at 70°F
Species activity outlook by water temperature and season
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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)
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.
Other records on this page
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory