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At a Glance A "medium concentration" of algae linked to red tide was confirmed in Atlantic waters.

Over the weekend, beachgoers further north complained of respiratory, eye and skin irritation.

Red tide is found almost exclusively in the Gulf of Mexico, but it has reached as far north as Delaware in the Atlantic.

King tides over the weekend are expected to cause at least some minor flooding from the Mid-Atlantic states.

Officials in Miami are warning residents to avoid king tide floodwaters expected to inundate coastal cities over the weekend because the waters could contain the toxic red tide algae that was detected earlier this week off Florida's southern Atlantic Coast.

Health departments have long warned residents to avoid making contact with king tide floodwaters because studies show the flooding waters pick up pollutants from the road and leaky septic tanks. But, now the added risk of possible toxic algae in the floodwaters has led officials in the city of Miami to issue heightened warnings , the Miami Herald reports.

“I’m hoping its going to be dead by then, but you can’t count on it,” Stephen Leatherman, a coastal environmental scientist at Florida International University, told the newspaper. “I’m hoping for the best.”

King tides, a colloquial term often used to describe exceptionally high tides that typically arise during a new or full moon and when the moon is at its perigee every 28 days, are expected to cause at least some minor flooding from the Mid-Atlantic states through South Florida over the weekend.

The moon reaches perigee, its closest point of approach to the earth, on Friday, Oct. 5, and it hits the new moon phase on Monday, Oct. 8. This results in what is known as a perigean spring tide .

The National Ocean Service says the Mid-Atlantic and southeastern states could see minor tidal flooding in low-lying areas along the coast.

Miami-Dade Beaches to Reopen



Meanwhile, Miami-Dade beaches that were closed on Thursday will reopen Friday but with warnings to beachgoers after tests confirmed red tide was found in ocean waters , according to local news reports.

The decision to reopen the beaches came after local officials met with state environmental officials, the Miami Herald reports.

A "medium concentration" of algae linked to red tide was confirmed in lab tests from Haulover Inlet, which connects Biscayne Bay with the Atlantic Ocean, Miami-Dade Mayor Carlos Gimenez told the Miami Herald. It is believed the algae made its way from the Gulf.

Just south of Haulover, tests from Miami Beach and Key Biscayne showed levels too low to prompt beach closures.

While red tide is rare on Florida's Atlantic Coast, officials confirmed that it had reached waters off of Palm Beach County Monday evening. Testing was expanded along the East Coast, including four beaches in Miami-Dade County and sections of Broward County, as well as waters two miles offshore.

“Whenever news goes out around the country that there’s a red tide in Miami-Dade County, yeah, it’s gonna have a some impact,” Gimenez said. “There was a moderate level north of Haulover, so we took the decision, look, let’s close the beach down and take all the precautions and let’s actually talk to the folks on the west coast.”

How long the tide will last depends on the amount of algae, winds and the current. If the coastal currents are moving the tide, it's possible conditions will worsen along beaches south of the affected areas.

The Florida Fish and Wildlife Conservation Commission said Sunday that it had detected "low to medium concentrations of naturally occurring red tide" in water samples taken off the coast of Palm Beach County after a number of people complained of respiratory, skin and eye irritations while at Atlantic beaches over the weekend.

<img class="styles__noscript__2rw2y" src="https://dsx.weather.com/util/image/w/longestredtide.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0" srcset="https://dsx.weather.com/util/image/w/longestredtide.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 400w, https://dsx.weather.com/util/image/w/longestredtide.jpg?v=ap&w=980&h=551&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 800w" > Florida's longest documented red tide blooms, according to its harmful algal bloom monitoring database. (Florida Fish and Wildlife) (Florida Fish and Wildlife)

Red tide has plagued beaches on Florida's southwest Gulf Coast since last fall. In August, Gov. Rick Scott declared a state of emergency because of the algae bloom. In mid-September, red tide caused a massive fish kill on Pinellas County beaches. The lingering bloom also has killed fish, manatees, dolphins, and sea turtles in Monroe, Collier, Charlotte, Lee, Sarasota, and Manatee counties.

Karenia brevis, the organisms that cause red tide are almost exclusively found in the Gulf of Mexico, according to the Florida Fish and Wildlife Conservation Commission, but beaches along the Atlantic coast are not immune.

The Palm Beach County release said of 57 occurrences of red tide in the Gulf of Mexico since 1953, eight have made their way to the East Coast in the area of Palm Beach County. All eight originated in the gulf and were carried by currents to the East Coast, the release said.

Red tide is not the same as the outbreak of toxic blue-green algae that began in Lake Okeechobee and spilled into the lake's estuaries across much of South Florida this summer.

Red Tides are naturally occurring algae blooms that form in marine water, while blue-green algae blooms are caused by cyanobacteria and form in fresh water.

According to the FWC, blue-green algae blooms originate from runoff containing human waste and fertilizers from nearby farms and neighborhoods. Nitrogen and phosphorus, as well as other nutrients in the polluted runoff, can act like fertilizer for the algae, creating large and long-lasting blooms.