Beach · Marin County · CA
Is Shell Beach - SHELL BEACH safe to swim?
No advisory or algae bloom reported for this water today.
Updated July 19, 2026 · California beach program (EPA BEACON)
SwimZone for iPhone · launching soon
Know before you get in at Shell Beach - SHELL BEACH.
Get an alert the day a bacteria or algae advisory goes up.
What's in the water at Shell Beach - SHELL BEACH right now
As of July 19, 2026, Shell Beach - SHELL BEACH in Marin County, California 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 0.0 in, which can wash bacteria and nutrients into the water.
Blue-green algae at Shell Beach - SHELL BEACH
Shell Beach - SHELL BEACH is a lake in Marin County, California. 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 Shell Beach - SHELL BEACH
- Is it safe to swim in Shell Beach - SHELL BEACH right now?
- Shell Beach - SHELL BEACH 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 Shell Beach - SHELL BEACH have blue-green algae (cyanobacteria)?
- Blue-green algae are not currently monitored at Shell Beach - SHELL BEACH. Watch for green, blue-green, or paint-like scum and avoid the water if you see it.
- Can dogs swim in Shell Beach - SHELL BEACH?
- No bloom is detected at Shell Beach - SHELL BEACH 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 California lakes and beaches have swim advisories today?
- Today, 28 California waters are under a swim advisory and 4 more warrant caution, out of 452 monitored waters SwimZone tracks in the state.
- How is Shell Beach - SHELL BEACH'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 Shell Beach - SHELL BEACH, and a recent-rainfall overlay, all refreshed daily. It was last updated July 19, 2026.