The conservation practices are not monitored and have not been kept up. One recent account suggests that the seasonal algae blooms in Lake Erie were possibly caused by runoff from cities, fertilizers, zebra mussels, and livestock near water. A second report focuses on the zebra mussels as being the cause of dead zones since they filter so much sediment that this produces an overgrowth of algae. One report suggests the oxygen-poor zone began about 1993 in the lake's central basin and becomes more pronounced during summer months, but it is somewhat of a mystery why this happens. Some scientists speculate that the dead zone is a naturally occurring phenomenon. Another report cites Ohio's Maumee River as the main source of polluted runoff of phosphorus from industries, municipalities, tributaries and agriculture, and in 2008, satellite images showed the algal bloom heading toward Pelee Island. There have been two-year $2 million studies trying to understand the "growing zone" which was described as a 10-foot-thick layer of cold water at the bottom, in one area, which stretches across the lake's center. It kills fish and microscopic creatures of the lake's food chain and fouls the water, and may cause further problems in later years for sport and commercial fishing.