Reservoir · Fairfield County · SC
Is Monticello Reservoir safe to swim?
Blue-green algae looks elevated by satellite; use caution and check local advisories.
Updated August 20, 2026 · EPA CyAN satellite
No bacteria advisory or sampling for this water.
Satellite imagery shows an elevated blue-green algae signal, below bloom levels and unconfirmed by sampling. Watch for scums and discoloration and check local advisories.
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Conditions at Monticello Reservoir are borderline right now.
Get a push the moment it tips into an advisory, and again the day it clears.
What's in the water at Monticello Reservoir right now
As of August 20, 2026, Monticello Reservoir in Fairfield County, South Carolina carries a swim caution. EPA's CyAN satellite showed an elevated blue-green algae signal here (August 19, 2026), below bloom levels and unconfirmed by sampling. 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 Monticello Reservoir
Monticello Reservoir is a reservoir in Fairfield County, South Carolina covering about 10.4 sq mi, the 8th-largest of the 16 lakes SwimZone monitors in South Carolina. EPA's CyAN satellite showed an elevated blue-green algae signal here (August 19, 2026), below bloom levels and unconfirmed by sampling. Larger, warmer waters like this can hold a bloom for weeks once nutrients and calm weather line up.
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 Monticello 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, Monticello Reservoir has shown a satellite-estimated bloom-level signal in 2 of them, most recently in June 2025. Those signals have been occasional rather than annual. Its highest satellite estimate was about 570,000 cells/mL in June 2022. These are satellite estimates, not water samples or posted advisories; check your state or county health department for official status.
When to swim at Monticello Reservoir
It is currently peak season for blue-green algae, when warm, calm water lets blooms form fastest. This lake has bloomed in 2 of 7 monitored summers, historically peaking around June. 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 Monticello Reservoir
- Is it safe to swim in Monticello Reservoir right now?
- Monticello Reservoir carries a swim caution today. EPA's CyAN satellite showed an elevated blue-green algae signal here (August 19, 2026), below bloom levels and unconfirmed by sampling. Conditions can change quickly with wind, heat, and rain, so check the posted signs and look at the water before you get in.
- Does Monticello Reservoir have blue-green algae (cyanobacteria)?
- Elevated but below bloom levels. EPA's CyAN satellite showed an elevated blue-green algae signal at Monticello Reservoir on August 19, 2026, unconfirmed by sampling. Keep an eye out for surface scum, which can concentrate quickly.
- Can dogs swim in Monticello Reservoir?
- Use caution. EPA's CyAN satellite estimated elevated blue-green algae at Monticello Reservoir on August 19, 2026 (a satellite estimate, not confirmed by sampling). Dogs are far more sensitive to cyanobacteria than people, so keep them out of the water and away from surface scum, and check local advisories.
- How often does Monticello Reservoir have blue-green algae blooms?
- Over 7 summers of EPA CyAN satellite imagery since 2020, Monticello Reservoir has shown a satellite-estimated bloom-level signal in 2 of them, most recently in June 2025. Those signals have been occasional rather than annual. Its highest satellite estimate was about 570,000 cells/mL in June 2022. These are satellite estimates, not water samples or posted advisories; check your state or county health department for official status.
- How many South Carolina lakes and beaches are unsafe for swimming today?
- Today, 0 South Carolina waters are above a safe-contact threshold and 11 more warrant caution, out of 36 monitored waters SwimZone tracks in the state.
- How is Monticello 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 Monticello Reservoir, and a recent-rainfall overlay, all refreshed daily. It was last updated August 20, 2026.
Before you swim: the basics
Swim spots near Monticello Reservoir
All South Carolina →Of the 6 monitored waters nearest Monticello Reservoir, 1 is flagged today.
| Water | Distance | Today | Algae read | Sampled |
|---|---|---|---|---|
| Parr Shoals ReservoirReservoir · Newberry County | 3.2 mi | No advisory | None detected | Jul 21 |
| Lake MurrayLake · Lexington County | 18 mi | No advisory | None detected | Aug 19 |
| Cedar Creek ReservoirReservoir · Lancaster County | 29 mi | No advisory | None detected | Aug 19 |
| Wateree LakeLake · Kershaw County | 29 mi | No advisory | None detected | Aug 19 |
| Fishing Creek ReservoirReservoir · Lancaster County | 32 mi | Use caution | Possible bloom | Aug 19 |
| Lake GreenwoodLake · Laurens County | 41 mi | No advisory | None detected | Aug 19 |