Dyer Reservoir: toxic algae advisories
Dyer Reservoir, Alameda County. See all Alameda County waters.
What the state's records say
The state's latest record, from Oct 19, 2026, recommends no advisory.
That reflects what the state knew on that date. It is not a finding that the water is safe now: blooms can return within days, and many are never reported.
Before you go, check the state's official algae page and any signs posted at the water.
Dogs at Dyer Reservoir
The state's latest record, from Oct 19, 2026, recommends no advisory. For Dyer Reservoir, that is not the same as an all-clear for today. Look at the water before your dog goes in: keep it out of green, blue-green or scummy water and away from mats on the shore.
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 |
|---|---|
| Outlet | The state's latest record, from Oct 19, 2026, recommends no advisory. |
Advisory history
Every advisory record the state has published for Dyer Reservoir, 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 |
|---|---|---|---|
| Oct 19, 2026 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Oct 2, 2026 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Sep 15, 2026 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Sep 10, 2026 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Jul 29, 2026 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Jul 10, 2026 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Jun 30, 2026 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Jun 12, 2026 | Outlet | None | Testing results below posting triggers; Updates from routine monitoring program-organization |
| May 22, 2026 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| May 1, 2026 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| May 1, 2026 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Oct 14, 2025 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Oct 2, 2025 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Sep 15, 2025 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Sep 2, 2025 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Aug 18, 2025 | Outlet | None | Updates from routine monitoring program-organization |
| Jul 25, 2025 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Jul 11, 2025 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Jun 30, 2025 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Jun 11, 2025 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| May 23, 2025 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Apr 25, 2025 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Sep 26, 2024 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Sep 5, 2024 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Aug 20, 2024 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Jul 12, 2024 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Jun 28, 2024 | Outlet | None | Testing results below posting triggers; Updates from routine monitoring program-organization |
| Jun 14, 2024 | Outlet | None | Testing results below posting triggers; Updates from routine monitoring program-organization |
| May 23, 2024 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Apr 25, 2024 | Outlet | None | Updates from routine monitoring program-organization; Visual monitoring only-absent bloom |
| Oct 16, 2023 | Outlet | None | Updates from routine monitoring program-organization |
| Oct 16, 2023 | Outlet | None | Updates from routine monitoring program-organization |
| Sep 29, 2023 | Outlet | None | Updates from routine monitoring program-organization |
| Sep 15, 2023 | Outlet | None | Updates from routine monitoring program-organization |
| Aug 31, 2023 | Outlet | None | Updates from routine monitoring program-organization |
| Aug 15, 2023 | Outlet | None | Updates from routine monitoring program-organization |
| Jul 14, 2023 | Outlet | None | Advisory based on visual and toxins; Updates from routine monitoring program-organization |
| Jun 23, 2023 | Outlet | None | Testing results below posting triggers; Updates from routine monitoring program-organization |
| May 25, 2023 | Outlet | None | Updates from routine monitoring program-organization |
| Nov 1, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Oct 17, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Sep 30, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Sep 16, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Sep 8, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Aug 30, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Aug 24, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Aug 18, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Jul 29, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Jul 15, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Jun 27, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Jun 14, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Jun 1, 2022 | Outlet | None | Updates from routine monitoring program-organization |
| Apr 28, 2022 | Outlet | None | Updates from routine monitoring program-organization |
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.