Some waters are experiencing errors processing till that waters to be waste disposal which resulted in the loss of existing potential, affect water quality and further on the presence of organisms present in the water, especially plankton (phytoplankton) which is the first organisms respond to changes in water quality. One of the pollutants in the water is mud Lapo in Porong, Sidoarjo. This research aims to identify phytoplankton in polluted waters, lapindo mud Porong, Sidoarjo. The method used is the method description. The analysis of samples carried out in the laboratory of Ecology