You are looking at the outfall of a sedimentation basin that is used to help take out sediments from the I-691 highway. Runoff from the highway is collected in the basin and discharged at an engineered rate to allow the suspended sediments such as road sand to settle out. This helps prevent the sediments from flowing directly into the river. Although there is natural sediment in the river, unnatural sediment from runoff can cause problems for fish and other organisms. Also, many pollutants travel by “hitching a ride” onto road sediment particles.