The Riverside Yacht Club, on the east side of Cos Cob Harbor and about 0.5 mile below the first bridge, is prominent.
Several marinas and boatyards are along the west side of the river from above the railroad bridge to the head of navigation.
Cos Cob Harbor, on the northeast side of Captain Harbor, has a dredged channel through it which extends 1.3 miles northward through the Mianus River to the head of navigation at Mianus. In 2003, the controlling depth was 6 feet at midchannel to the bascule railroad bridge, thence 2.8 feet (4.8 feet at midchannel) to the fixed highway bridge, thence 4.8 feet at midchannel (except for shoaling to 1.1 feet in the last 300 feet of the dredged channel) to the head of navigation at Mianus. Shoaling is reported to be abrupt along both edges of the channel. The channel is buoyed to the first bridge; above this point the channel may be followed by steering a midchannel course between the marsh banks.
There are several dangers off the entrance of Cos Cob Harbor that must be avoided; most are buoyed. These include Newfoundland Reef, covered 4 feet, a mile northeastward of Little Captain Island; Red Rock, which uncovers 7 feet, 0.5 mile west of Newfoundland Reef; Hitchcock Rock, awash at low water, 0.3 mile northwestward of Newfoundland Reef; and Pecks Rock, bare at low water, 0.2 mile north of Hitchcock Rock.
Mianus River is crossed by a railroad bascule bridge with a clearance of 20 feet, and by a highway fixed bridge with a clearance of 45 feet, about 0.4 mile to the northward.