Benthic algae densely cover the bed of Fishing Creek, their preponderance attributed to leaking septic systems. At one location on the main stem downstream of Grassmere Park, coverage exceeds 60 percent. The dominant algal organism on West Branch Fishing Creek near the village of Elk Grove is "Cladophora". The green algae "Tetraspora" dominates the stretch of Fishing Creek for downstream of Grassmere Park, where it covers 80 percent of the riverbed. South of Pennsylvania Route 239's crossing of the creek, the dominant algal organisms are "Microspora", "Mougeotia", and "Spirogyra". In the fall, decomposing algae covers 50 percent of the riverbed.