A red tide that has sloshed up and down the Gulf Coast for nearly a year, leaving a wake of dead sea life, murky water and stinky beaches, has now landed on the state’s most crowded shores in Miami-Dade County.

Following confirmation late Wednesday night that the algae that causes red tide had been detected at moderate levels, county officials closed beaches north of Haulover Park before dawn Thursday. The decision was made following a meeting with state environmental and health officials, Mayor Carlos Gimenez said in a statement. Later Thursday, the county said the beaches would reopen Friday.

People with severe or chronic respiratory conditions should continue to keep away, he said. Signs will be placed at beaches warning visitors about potential risks.

On Thursday, tests found red tide on four beaches. While far milder than what’s appeared on the west coast — algae levels that cause the saltwater blooms have climbed only to moderate so far along one beach — the spread raises concerns about a deepening crisis in a state already battling a summer-long freshwater blue-green algae bloom in Lake Okeechobee and coastal rivers.