(Bloomberg) -- Large numbers of endangered seahorses as well as rare abalone and other shellfish washed up on beaches in South Africa’s Western Cape province after floods from a storm that brought record rainfall.

The floodwater from swollen rivers diluted the seawater close to the coast, weakening the animals, the Department of Forestry, Fisheries and the Environment said in a statement on Friday. Fish and rock lobsters were able to move further offshore, but slower and immobile invertebrates were not and became stressed by the fresher water, causing them to beach, the department said. 

A “substantial number of seahorses” washed up on a beach about 520 kilometers (323 miles) east of Cape Town and were collected and taken for rehabilitation, the department said. The area is home to Knysna seahorses which are found in only three estuaries and are one of the world’s most endangered seahorse species, according to the International Union for Conservation of Nature.

The weekend storm in the coastal province killed 11 people, displaced thousands of others, washed away bridges and blocked access to Cape Town along major routes. It’s likely that other unusual washouts of sea animals will occur over the next week as floodwater moves toward the sea, the department said.

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