Shasta Lake: toxic algae advisories
Shasta Lake, Shasta County. See all Shasta County waters.
What the state's records say
Caution advisory, last posted Sep 9, 2016. No all-clear recorded.
11 reported spots here have an advisory with no all-clear recorded.
Reporting is voluntary, so the state may not have recorded an end even if conditions changed. Check posted signs and the official map.
What this level asks: Algae that can make toxins may be present. Keep people, children and pets away from algae and scum, and do not let pets drink the water.
Before you go, check the state's official algae page and any signs posted at the water.
Dogs at Shasta Lake
The state has an advisory on file for Shasta Lake (Caution advisory), last posted Sep 9, 2016, and no all-clear recorded. Keep your dog out of the water and away from scum on the shore until the state records an end.
Satellite estimate (not an advisory)
No satellite reading on file for Shasta Lake in recent weeks. Clouds, ice, or a lake shape the satellite's estimate near its center misses can cause this. It is a gap in the data, not a reading.
This is a satellite estimate from the U.S. EPA's Cyanobacteria Assessment Network, not an advisory. It estimates how much cyanobacteria is in the water near the lake's center, not whether toxins are present: a high number does not mean toxins, and a low one does not mean there are none. It covers lakes of about 1 square kilometer and larger, so small ponds, dog parks and most rivers are not covered, and clouds can hide a lake for weeks. It never changes the advisory status above.
Satellite estimates: U.S. EPA Cyanobacteria Assessment Network (CyAN), from Copernicus Sentinel-3 data. Provisional, research-level estimates; EPA does not endorse this site. Checked Oct 22, 2026.
Reported spots
The state records each report at a spot, such as a beach or a boat ramp. Each spot's latest deciding record:
| Spot | Status |
|---|---|
| Silverthorn resort | The state's latest record, from Jul 24, 2026, recommends no advisory. |
| Silverthorn Resort | The state's latest record, from Jul 24, 2026, recommends no advisory. |
| Pit River Arm | The state's latest record, from Apr 16, 2021, recommends no advisory. |
| Shasta Lake/Pit River Arm | Caution advisory, last posted Sep 9, 2016. No all-clear recorded. |
| Shasta Lake - Sacramento Arm | Caution advisory, last posted Sep 2, 2016. No all-clear recorded. |
| Shasta Lake - McCloud Arm | Caution advisory, last posted Sep 2, 2016. No all-clear recorded. |
| Shasta Lake - Holiday Harbor | Caution advisory, last posted Sep 2, 2016. No all-clear recorded. |
| Shasta Lake - Digger Bay | Caution advisory, last posted Sep 2, 2016. No all-clear recorded. |
| Shasta Lake - Bridge Bay | Caution advisory, last posted Sep 2, 2016. No all-clear recorded. |
| Shasta Lake - Squaw Arm | Caution advisory, last posted Sep 2, 2016. No all-clear recorded. |
| Shasta Lake - Silverthorn | Caution advisory, last posted Sep 2, 2016. No all-clear recorded. |
| Shasta Lake - Jones Valley | Caution advisory, last posted Sep 2, 2016. No all-clear recorded. |
| Shasta Lake - O'Brien area | Caution advisory, last posted Aug 24, 2016. No all-clear recorded. |
| Shasta Lake - Antlers Area | Caution advisory, last posted Aug 24, 2016. No all-clear recorded. |
Advisory history
Every advisory record the state has published for Shasta Lake, newest first. "None" is the state's record that no advisory was recommended on that date. "NA" records do not change a status.
| Date | Spot | State's level | Notes |
|---|---|---|---|
| Jul 24, 2026 | Silverthorn resort | None | Testing results below posting triggers |
| Jul 24, 2026 | Silverthorn Resort | None | Testing results below posting triggers |
| Jul 16, 2026 | Silverthorn Resort | NA - refer to Report Details | Suspected illness reported |
| Jul 14, 2026 | Silverthorn resort | NA - refer to Report Details | Suspected illness reported |
| Jul 14, 2026 | Silverthorn resort | NA - refer to Report Details | Suspected illness reported |
| Apr 16, 2021 | Pit River Arm | None | Testing results below posting triggers |
| Sep 9, 2016 | Shasta Lake/Pit River Arm | Caution | |
| Sep 2, 2016 | Shasta Lake - Sacramento Arm | Caution | |
| Sep 2, 2016 | Shasta Lake - McCloud Arm | Caution | |
| Sep 2, 2016 | Shasta Lake - Holiday Harbor | Caution | |
| Sep 2, 2016 | Shasta Lake - Digger Bay | Caution | |
| Sep 2, 2016 | Shasta Lake - Bridge Bay | Caution | |
| Sep 2, 2016 | Shasta Lake - Squaw Arm | Caution | |
| Sep 2, 2016 | Shasta Lake - Silverthorn | Caution | |
| Sep 2, 2016 | Shasta Lake - Jones Valley | Caution | |
| Aug 24, 2016 | Shasta Lake - O'Brien area | Caution | |
| Aug 24, 2016 | Shasta Lake - Antlers Area | Caution |
Source
Advisory data: California State Water Resources Control Board, Freshwater Harmful Algal Bloom Program, via data.ca.gov (public domain). Advisories are recommendations; reporting is voluntary and incomplete. The state's data. An advisory ends only when the state records a later "None" (no advisory recommended) at the same spot, or an end date. A blank end date is unknown.