There's something distinctly fishy in the air as the big stink hits Los Angeles

Something is rotten in the state of California, where public safety experts are attempting to identify the source of a foul smell which is polluting Los Angeles and its suburbs.

The stench has prompted at least 200 emergency calls by residents. Most appear to be under the impression that either a sewage main has broken or a toxic spill occurred in their neighbourhood.

Experts believe that the pungent aroma – part sulphur, part rotten eggs – is coming from the Salton Sea, a vast inland lake 150 miles south-east of Los Angeles, where large numbers of fish were reported to have died last week. Strong winds have added to the problem by churning up the shallow water, exposing a layer of mud formed from decaying plants, fish, and other animals.

"It's very unusual," said a spokesman for the South Coast Air Quality Management District (AQMD). "Several factors indicate that the Salton Sea may have been the source of these odours." The sea was formed in 1905, when the Colorado River burst its banks. It covers 360 sq miles, sits 200ft below sea level, is highly saline and has been slowly evaporating in recent decades. That often exposes areas of bubbling mud which cause localised sulphurous smells.

It's highly unusual for those smells to travel, however. But the AQMD believes strong winds, high temperatures and unique pressure systems helped the odour to reach towns and cities.

The smell was bad enough for schools to keep pupils indoors during break time. The Los Angeles Fire Department went on radio to ask residents to stop calling 911.