Every summer for more than 30 years, massive quantities of green algae have been washing up on parts of the French coastline. Once washed up on beaches, these algae deposits decompose and produce large quantities of gases, especially hydrogen sulfide (H2S), potentially exposing walkers, local residents and workers required to collect these algae, to risks. Beaches in France's Brittany region have been repeatedly affected and are continually monitored for new growth. Nitrates that drain into water as a result of intensive farming are blamed for the killer algae. Brittany has a high concentration of pig, cattle and poultry farming. The excessive algae growth has also caused several allegations of illness and even deaths.