BTL floating covers, or float covers, placed on top of lagoons, ponds or tanks (as floating tank covers) can serve a variety of purposes including the following: evaporation reduction. fume and odor reduction. containment or collection of gasses. thermal insulation of covered liquids. protection against contamination. separation of rain water or snow melt from contained liquids. additional protection of people and wildlife from contaminated substances. water security, which is attained by providing a physical barrier to vandalism, terrorism, etc.