The creek flows generally to the north and discharges into Lake Ontario, through Olcott Harbor, approximately 18 miles (29 km) east of the mouth of the Niagara River.

The main branch of Eighteen Mile Creek originates southeast of the City of Lockport, in the vicinity of Keck and Chestnut Ridge Roads, on the south side of the Niagara Escarpment.

As the creek descends the escarpment, it travels through the abandoned Flintkote factory property on Mill Street, and adjacent to the Lockport Wastewater Treatment Plant.

These contaminants include but are not limited to: polychlorinated biphenyls (PCBs), mercury, dioxins and furans, dieldrin, mirex, DDT, lead, and copper.

The extensive beds of emergent and submergent aquatic vegetation in this area account for an estimated 65 acres (260,000 m2), comprising one of the largest coastal wetlands in the western portion of Lake Ontario.

These wetlands and undisturbed woodlands bordering Eighteen Mile Creek provide valuable habitats for wildlife that are uncommon in Niagara County's coastal area.

Specific goals of the RAP are the protection and enhancement of human health, fish and wildlife, aesthetics, recreation and the economy of the Eighteen Mile Creek Area of Concern.

Bathing and aquatic life have been established as the best uses of Eighteen Mile Creek through a public process under the New York State Stream Classification System.