Is the water at Key Biscayne safe to swim today?

What the readings mean

Florida DOH samples coastal waters weekly for Enterococcus, a bacteria found in human and animal waste. Elevated readings flag potential fecal contamination — usually from stormwater runoff after heavy rain, or from a sewer break upstream. The unit is CFU (colony-forming units) per 100 milliliters of seawater.

The thresholds DOH uses:

• Good — 0 to 35.4 CFU/100mL. Normal background. Swim freely.
• Moderate — 35.5 to 70.4 CFU/100mL. Elevated, but below the action threshold.
• Poor — 70.5 or higher. A single Poor reading doesn't automatically trigger an advisory — DOH looks at the geometric mean across recent samples and may re-sample before issuing one.

What an "advisory" actually means

An active advisory means DOH has formally recommended against water-related activities at that specific beach. Advisories are issued when repeat sampling confirms elevated bacteria, not just one bad reading. They stay in effect until two consecutive samples come back clean.

The advisory only covers the named beach — Crandon Park North, Crandon Park South, Cape Florida Park, and the Village beach are each sampled separately. An advisory at Crandon North says nothing about Cape Florida 3 miles south.

The May 2026 Crandon North story

A good illustration of how the system works played out in late May 2026:

• May 19: Crandon North sampled at 98 CFU/100mL (Poor) — no advisory yet.
• May 20: Re-sample came back at 156 CFU (still Poor). DOH-Miami-Dade issued an advisory on May 22.
• May 22: Follow-up sample at 72 CFU (Poor, but lower).

Meanwhile Crandon South, less than a mile away, never went into advisory — its samples stayed Good throughout. That separation is why we show every KB beach on the home page rather than a single overall status. The current advisory state for each beach is what we pull directly from the live DOH dashboard, so you'll always see the up-to-date picture above rather than a frozen timeline.

What causes high readings

Most KB advisories trace back to one of three things:

• Heavy rain within the past 24–48 hours, which flushes pet waste and street runoff into the bay through stormwater outflows.
• Boat discharge in shallow water, especially during long holiday weekends when anchoring on the sandbar peaks.
• Sewer-main issues on the island or upstream in Miami — rare, but they make headlines when they happen.

The Village's stormwater and resiliency program is partly aimed at reducing the rain-runoff signal over time.

Where to swim when there's an advisory

If your usual beach is under an advisory, your safest swap is the closest beach that isn't. The four KB beaches DOH tracks are usually independent. The home page shows the most recent reading for each — pick a Good or Moderate beach within walking distance.

Hobie Beach on the causeway is technically Virginia Key, not Key Biscayne proper, and the bay side has different runoff patterns — it doesn't always mirror the Atlantic-facing beaches. Cape Florida (the state park at the south tip) is the southernmost option if Crandon is under an advisory. The latest sample for each location is always on the home page.

Source

Samples on this page come directly from the Florida Department of Health beach-water-quality dashboard. Nothing is interpreted or estimated — what we show is the same number DOH published, refreshed every 30 minutes.