Reservoir · Modoc County · CA
Is Lower Roberts Reservoir safe to swim?
No advisory or algae bloom reported for this water today.
Updated August 20, 2026 · EPA CyAN satellite
No bacteria advisory or sampling for this water.
No blue-green algae bloom detected in the latest clear satellite image. This is a satellite estimate, not a safety guarantee, and does not replace an official advisory.
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What's in the water at Lower Roberts Reservoir right now
As of August 20, 2026, Lower Roberts Reservoir in Modoc County, California has no advisory posted. EPA's CyAN satellite detected no blue-green algae bloom in the latest clear image (August 19, 2026), which is an estimate, not a guarantee. Modeled rainfall over the past week was about 0.0 in (Open-Meteo, a gridded estimate that can differ from a local gauge), which can wash bacteria and nutrients into the water.
Blue-green algae at Lower Roberts Reservoir
Lower Roberts Reservoir is a reservoir in Modoc County, California covering about 0.8 sq mi, the 139th-largest of the 186 lakes SwimZone monitors in California. EPA's CyAN satellite detected no blue-green algae bloom in the latest clear image (August 19, 2026), which is an estimate, not a guarantee.
Blue-green algae (cyanobacteria) blooms are most common from midsummer into early fall, when the water is warm, calm, and rich in nutrients from runoff. They can produce toxins that make people sick and can be rapidly fatal to dogs, so skip water that looks green, scummy, or like spilled paint, and keep children and pets out of it.
Bloom history at Lower Roberts Reservoir
From EPA CyAN's satellite archive
Each bar is that summer's peak EPA CyAN satellite estimate (log scale); the red cap is the part above the bloom-level threshold. Satellite estimates, not water samples or posted advisories.
Over 7 summers of EPA CyAN satellite imagery since 2020, Lower Roberts Reservoir has shown a satellite-estimated bloom-level signal in 1 of them, most recently in August 2023. Those signals have been occasional rather than annual. Its highest satellite estimate was about 2,800,000 cells/mL in August 2023. These are satellite estimates, not water samples or posted advisories; check your state or county health department for official status.
When to swim at Lower Roberts Reservoir
It is currently peak season for blue-green algae, when warm, calm water lets blooms form fastest. This lake has bloomed in 1 of 7 monitored summers, historically peaking around August. Early summer, before the water fully warms, has generally been the safer window here; check the current read before you go either way.
Frequently asked: swimming in Lower Roberts Reservoir
- Is it safe to swim in Lower Roberts Reservoir right now?
- Lower Roberts Reservoir has no advisory posted today. EPA's CyAN satellite detected no blue-green algae bloom in the latest clear image (August 19, 2026), which is an estimate, not a guarantee. Conditions can change quickly with wind, heat, and rain, so check the posted signs and look at the water before you get in.
- Does Lower Roberts Reservoir have blue-green algae (cyanobacteria)?
- EPA's CyAN satellite detected no blue-green algae bloom at Lower Roberts Reservoir in the latest clear image (August 19, 2026). This is a satellite estimate below the sensor's detection limit, not a guarantee: cyanobacteria can appear within hours in warm, calm, nutrient-rich water, so look before you swim.
- Can dogs swim in Lower Roberts Reservoir?
- No bloom is detected at Lower Roberts Reservoir today, but dogs are much more vulnerable to blue-green algae than people, and blooms can form within hours. Always keep dogs away from water that looks green, scummy, or discolored, and rinse them off after swimming.
- How often does Lower Roberts Reservoir have blue-green algae blooms?
- Over 7 summers of EPA CyAN satellite imagery since 2020, Lower Roberts Reservoir has shown a satellite-estimated bloom-level signal in 1 of them, most recently in August 2023. Those signals have been occasional rather than annual. Its highest satellite estimate was about 2,800,000 cells/mL in August 2023. These are satellite estimates, not water samples or posted advisories; check your state or county health department for official status.
- How many California lakes and beaches are unsafe for swimming today?
- Today, 0 California waters are above a safe-contact threshold and 21 more warrant caution, out of 445 monitored waters SwimZone tracks in the state.
- How is Lower Roberts Reservoir's water quality measured?
- SwimZone builds this read from EPA CyAN satellite imagery for blue-green algae, official beach and fecal-bacteria advisories where a program monitors Lower Roberts Reservoir, and a recent-rainfall overlay, all refreshed daily. It was last updated August 20, 2026.
Before you swim: the basics
Swim spots near Lower Roberts Reservoir
All California →Of the 6 monitored waters nearest Lower Roberts Reservoir, 1 is flagged today.
| Water | Distance | Today | Algae read | Sampled |
|---|---|---|---|---|
| Horr PondPond · Shasta County | 17 mi | No advisory | None detected | Aug 19 |
| Beeler ReservoirReservoir · Modoc County | 19 mi | No advisory | None detected | Aug 19 |
| Coyote ReservoirReservoir · Lassen County | 25 mi | No advisory | None detected | Aug 19 |
| Bayley ReservoirReservoir · Modoc County | 27 mi | No advisory | None detected | Aug 19 |
| Reservoir FReservoir · Modoc County | 27 mi | No advisory | None detected | Aug 19 |
| Lake BrittonLake · Shasta County | 29 mi | Use caution | Unconfirmed | Aug 19 |