Life is gross...
"In their natural habitat freshwater bryozoans contribute to nutrient cycling, and they are grazed upon by fish and certain invertebrates. However, they also are a nuisance when they grow inside pipelines and filters, blocking or seriously disrupting the flow of water in irrigation, wastewater, and cooling water systems. Any pipeline that carries untreated water from a lake or river is at risk of becoming fouled with bryozoan colonies."