Algae covered beach. Excessive growth of sea lettuce (green algae, Ulva sp.) covering Morieux beach, Brittany. Many beaches in Brittany are regularly affected by huge blooms of algae as a result of the leaching of fertilisers, primarily nitrates, from farms into the rivers. This causes an increase in the concentration of chemical nutrients in the ecosystem (eutrophication), which increases plant growth. Here there are signs warning of the poisonous fumes produced by the algae as it decays on the beach. Photographed at the mouth of the Gouessant river, Saint-Brieuc bay, Brittany, France.