MADRID — Spanish authorities are expanding a ban on harmful fertilizers around a saltwater lagoon on the country’s Mediterranean coast, where over the past 10 days several tons of dead fish have washed up.

The regional government of Murcia, some 400 kilometers (240 miles) southeast of Madrid, announced Wednesday that the use of inorganic nitrogen fertilizers at farms within 1,500 meters (1,640 yards) of the Mar Menor lagoon is to be prohibited.

Some of those fertilizers can cause algae blooms, which deplete oxygen in surface water, killing fish.

Murcia is one of Spain’s main producers of fruit and vegetables, with much of the produce exported to northern Europe.

The lagoon is a well-known beauty spot and is popular for vacations.

The Murcia government estimates that every day around 5 metric tons (5.5 tons) of fertilizer runoffs from nearby farms are washed into the lagoon.

Spain’s Ecology Minister Teresa Ribera visited the lagoon Wednesday and welcomed the regional government’s plan, which includes increasing and expediting financial penalties on offenders.

She said that of more than 400 sanctions currently imposed by authorities, some 200 are in court and more than 200 remain unresolved.