The florida everglades have declined in size and suffered from pollution due to overpopulation. when runoff occurs, a dense growth of algae forms along the water surface. if scientists analyzed the water, what would they most likely find in the runoff that contributes to so much growth?

The algal growth is because of pollution of the water body. The water being used by the population staying in the Everglades might have disposed of waste water from household specifically from sewage, agricultural irrigation containing pesticides or insecticides. These human activities could add up minerals in the water which can facilitate the growth of algae. These can be responsible for eutrophication of water body in which the extensive algal growth depletes the oxygen concentration in water and responsible for death of aquatic organisms.  

this is true, assuming that the allele is completely recessive and incomplete dominance is not a factor.