Beach · Calvert County · MD
Is Flag Harbor safe to swim?
No advisory or algae bloom reported for this water today.
Updated July 19, 2026 · Maryland beach program (EPA BEACON)
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What's in the water at Flag Harbor right now
As of July 19, 2026, Flag Harbor in Calvert County, Maryland is clear to swim. Blue-green algae are not currently monitored at this water. No fecal-bacteria advisory is posted (state beach program). Rainfall over the past week totaled 0.2 in, which can wash bacteria and nutrients into the water.
Blue-green algae at Flag Harbor
Flag Harbor is a lake in Calvert County, Maryland. Blue-green algae are not currently monitored at this water.
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.
Frequently asked: swimming in Flag Harbor
- Is it safe to swim in Flag Harbor right now?
- Flag Harbor is clear to swim today. Blue-green algae are not currently monitored at this water. Conditions can change quickly with wind, heat, and rain, so check the posted signs and look at the water before you get in.
- Does Flag Harbor have blue-green algae (cyanobacteria)?
- Blue-green algae are not currently monitored at Flag Harbor. Watch for green, blue-green, or paint-like scum and avoid the water if you see it.
- Can dogs swim in Flag Harbor?
- No bloom is detected at Flag Harbor 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 many Maryland lakes and beaches have swim advisories today?
- Today, 0 Maryland waters are under a swim advisory and 10 more warrant caution, out of 66 monitored waters SwimZone tracks in the state.
- How is Flag Harbor'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 Flag Harbor, and a recent-rainfall overlay, all refreshed daily. It was last updated July 19, 2026.