Pets on a leash are allowed at Missouri National Recreational River, located on the border between Nebraska and South Dakota. Pets in South Dakota and Nebraska state parks must be on a leash at all times. However, they should not be leashed while in a boat or a canoe on the river. In Nebraska, pets must be on a leash no longer than 6 feet; in South Dakota, pets must be on a leash no longer than 10 feet. Pets are not permitted on designated swimming beaches or in any park buildings (including camping cabins, lodges and comfort stations).
More information on the Missouri National Recreational River pet policy
