De Mars Westhaven is the smaller of two marina basins at Camping & Jachthaven De Mars, a family-run combination campsite and marina situated within the 400-hectare recreation area known as Rhederlaag, near Lathum in Gelderland.

The facility lies in open connection with the IJssel river. The Westhaven was fully renovated in March 2020. Located on the western side of the campsite, the Westhaven sits close to several amenities including a playground, canteen, cafeteria, and supermarket.

The larger Oosthaven, on the eastern side, serves as the main transit berth and hosts the harbor office along with toilet facilities, showers, and laundry. The site operates seasonally, from April through October.