The First no swimming sign and advisories were posted in July 1962 along the New Orleans Lakefront due to pollution from sewage. By the late 1980s the advisories included the entire south shore and also covered the rivers on the north shore.
Currently there is still an advisory (not a ban) about swimming along the south shore of Lake. Sampling indicates that water quality conditions have greatly improved in the intervening decades since the advisories were introduced. Today south shore water quality is almost always suitable for swimming. Water quality is directly related to rainfall and associated runoff and discharges. If heavy rains occur, we recommend staying out of the water for two to three days.
The story is a bit different on the north shore. The rapid growth has introduced many new sources of pollution into bayous, rivers, and the Lake. The department of Health and Hospitals advises against swimming in the rivers or near the mouth of rivers. We believe people should wait at least three days after a rain on larger rivers like the Tchefuncte and Tangipahoa and should probably not swim in smaller bayous like Bayou Castine and Bayou Lacombe.