Attention to water quality was focused in South Florida in 1986 when a widespread algal bloom occurred in one-fifth of Lake Okeechobee. The bloom was discovered to be the result of fertilizers from the Everglades Agricultural Area.[31] Although laws stated in 1979 that the chemicals used in the EAA should not be deposited into the lake, they were flushed into the canals that fed the Everglades Water Conservation Areas, and eventually pumped into the lake.[11] Microbiologists discovered that, although phosphorus assists plant growth, it destroys periphyton, one of the basic building blocks of marl in the Everglades. Marl is one of two types of Everglades soil, along with peat; it is found where parts of the Everglades are flooded for shorter periods of time as layers of periphyton dry.[32] Most of the phosphorus compounds also rid peat of dissolved oxygen and promote algae growth, causing native invertebrates to die, and sawgrass to be replaced with invasive cattails that grow too tall and thick to allow nesting for birds and alligators.[33] Tested water showed 500 parts per billion (ppb) of phosphorus near sugarcane fields. State legislation in 1987 mandated a 40% reduction of phosphorus by 1992.