Flies and mosquitoes plague Porto and Matosinhos beaches as dead algae builds up

The phenomenon affecting the sands in Porto and Matosinhos is being driven by a build-up of dead algae on the beach.

Flies and mosquitoes on Porto and Matosinhos beaches

An invasion of flies and mosquitoes on the beaches of Porto and Matosinhos has been troubling beachgoers, with many people even leaving the shore because of the discomfort.

Why dead algae are washing up earlier this year

The problem is linked to dead algae accumulating on the sand. This usually happens between mid-August and September, but this year it has arrived sooner due to strong winds and differences in air temperature. The El Niño climate phenomenon is also having an effect.

What experts say: dead algae removal at low tide

According to hydrobiologist Adriano Bordalo e Sá, "there is no other solution except the physical removal of the algae that have washed ashore". Speaking to JN, the full professor at the Abel Salazar Institute of Biomedical Sciences explains that, underwater, there are countless brown and green algae attached to rocks, which end up detaching because of coastal upwelling caused by strong currents generated by the wind.

"Because of the strong currents, which are linked to the wind and temperature differences, the algae break free and end up on the beach," says Adriano Bordalo e Sá, noting that El Niño "also has an influence".

"The solution is daily removal of the algae at low tide," the hydrobiologist points out, reminding people that Porto’s beaches are under municipal management, with the exception of Praia Internacional. "With these temperatures, if the masses of algae are not removed, the eggs that flies lay hatch," leading to mosquitoes.

"On top of this problem, we also have gulls, which defecate everywhere. The dead algae plus the gull droppings create this breeding ground for insects," Bordalo e Sá adds.