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The presence of birds at retention/detention basins on or adjacent to an airport increases the probability of experiencing a wildlife strike. Overhead gridline systems have proven effective for reducing the presence of birds on small water bodies. While there are several grid materials available to address bird hazards associated with small basins, the list of options decreases quickly as the distance to be spanned increases. The Michigan Wildlife Services program (WS) tested five types of grid material on three large detention basins to determine which materials could span up to 675 meters (2214.5 feet) without center supports. Additionally, the line material could not sag substantially, because of water fluctuations of up to 1.5 meters (5 feet) depending on the frequency and duration of rain events. If a line would touch the surface of the water, the surface tension would hold it in place until freeze-up. The material found to be superior in our tests, was a braided fishing line made of Spectra® called PowerPro. Grid lines were suspended in two directions on 30-meter (100 foot) spacing. Preliminary results show a notable reduction in bird usage by waterfowl and gulls.