The “storm sewer” is a system designed to carry rainfall runoff and other drainage but not sewage. The runoff is carried in underground pipes or open ditches and discharges (untreated) into streams or other surface water bodies. The storm inlets (catch basins) to this system may be found in curbs and low-lying outdoor areas.

Disposal of chemicals or hazardous substances via the storm sewer system is not only illegal but damages the environment. Pollutants that get into storm drains can poison fish, birds, and other wildlife, and can find their way into drinking water supplies. In addition, silt, litter, and organic matter (branches, clippings, etc.) can clog storm drains and cause flooding. Common storm water pollutants may include: Motor Oil, Antifreeze/Chemicals, Fertilizer/Pesticides, Animal Waste, Soaps & Detergents, and Yard Waste.

The “sanitary sewer” is a system of underground pipes that carries sewage from bathrooms, sinks, kitchens, basemen drains, and other plumbing components to the Regional Wastewater Treatment & Resource Recovery Facility. The wastewater at the plant is treated and then discharged into Lake Winnebago.


A sewer backup creates a stressful and emotional situation for the homeowner/resident. In some cases it may cause health and safety concerns as well as property loss.

The City of Fond du Lac makes every effort to be responsive to a resident’s needs and concerns when a sewer backup occurs in the sanitary sewer line. The City has sewer crews that inspect, clean and maintain sewers on a daily basis. Unfortunately, because a sewer is not a closed system, many things put into the sewer can clog both the City’s sanitary sewer system and the private sanitary lateral. Other factors can cause backups as well, such as tree roots, which can grow into and obstruct the system.


If you experience a sewer problem call the City of Fond du Lac Department of Public Works (920) 322-3540 first and report the issue. Back up of sewage into your basement, back-up of sewer lines, lines that are broken, sewage odors and overflowing manholes are considered an emergency. After hours residents can call 920-322-3565 for the On-Call Foreman.


More often than not, the cause of a backup in your lateral or City sewer main is from items that the lines are not meant to handle, such as kid’s toys, clothing, towels, rags, diapers, paper products (other than toilet paper). Items you flush down your toilet may not affect you, but it might cause problems for your neighbors! Other possible causes could be roots or grease in the sewer lateral or main. Discharging sump pump or clear water into your basement floor drains or other facilities that discharge to the sanitary sewer is also prohibited. The sanitary sewer main is only sized to handle domestic waste flows not storm water or clear water. Storm water and clear water is supposed to drain to storm sewers. Old laterals may become fragile and brittle which could fail and cause blockages of debris or ground water into the private lateral. Leaves, sticks, rocks, bricks and trash are sometimes found down manholes and can also cause a backup.

FAQ – Basement Back-Ups