The Sleattemer Mar, also known as the Slotermeer, is one of the significant Frisian lakes in the southwest of Friesland, Netherlands. It sits between the three towns of Sloten, Balk, and Woudsend, and is counted among the largest and most important lakes in the broader Frisian Lakes region, which encompasses 24 lakes in Central and Southwest Friesland.

The lake is relatively shallow outside its main navigable channels. Three marked channels, indicated with buoys, connect Sloten, Balk, and Woudsend to one another; outside these channels, the water can be as little as 1.20 meters deep. Paddlers should be aware of this when planning routes away from the marked fairways, as shallow areas may limit passage depending on conditions.

A designated speed boating area exists within the lake, marked by yellow buoys, where motorized vessels are permitted to travel at high speeds. Outside these buoys, all watercraft — including motorboats — are required to reduce speed to accommodate other water users. Paddlers should remain aware of the speed boating zone and plan accordingly to avoid conflict with faster traffic.

The lake has historical significance as part of the Elfstedentocht route, the famous eleven-cities skating tour, which crosses the Sleattemer Mar twice — once between IJlst and Sloten, and again between Sloten and Stavoren. The surrounding area includes the village of Balk, described as the main town of Gaasterland with a range of amenities, and the historic town of Sloten (Sleat). There is a swimming and surfing beach at Balk (Zwem- en surfstrand Balk) as well as a beach known as De Baaier near the lake, which may be useful reference points for access or rest stops.

The lake sits within the Zuidwesthoek (Súdwesthoeke) region, an area with a distinct Frisian cultural identity. The surrounding landscape is characteristic of the flat Frisian countryside, with the lake serving as a hub for water sports activity among the three nearby towns.