Mortimer Slough is a body of water located in eastern South Dakota, forming part of the Oakwood Lakes chain near Bruce. The slough was named for Samuel "Ol' Spot" Mortimer, who arrived in the area in 1869 and built a log cabin that still stands in what is now Oakwood Lakes State Park.

The slough is part of a historic area between Lake Poinsett and Oakwood Lakes that served as a summer hunting ground for the Sioux for over hundred years. Today, it is one of several interconnected glacial lakes in the Oakwood Lakes system, which includes Lake Tetonkaha, Johnson Lake, Oakwood East, and Oakwood West.

Water Activities and Access: The area offers opportunities for paddling and other water activities through Oakwood Lakes State Park. While the park maintains boat access points, paddlers should check with park staff about the best launch points for accessing Mortimer Slough.

Wildlife and Natural Features: The region is rich in wildlife, particularly waterfowl, as it is designated as a waterfowl production area. Paddlers can expect to encounter various bird species throughout the season.

Historical Significance: The historical significance of Mortimer Slough is tied to its namesake, Samuel Mortimer, a shoemaker from New York who came to Dakota Territory after hearing stories of the rich fur trade in the Big Sioux Valley. His original log cabin, built in 1869, remains a testament to early European settlement in the area.

Park Access and Amenities: The slough can be accessed through Oakwood Lakes State Park, which offers various facilities including camping areas and a visitor center. The park entrance is located on Oakwood Drive, approximately one mile north of Brookings County Road 6.

Seasonal Considerations: The water bodies in this area typically freeze during winter months, making paddling a seasonal activity. Ice-out timing in spring and ice-in timing in fall should be considered when planning paddling trips.