Tisnaren, Spring-fed lake in Östergötland and Södermanland, Sweden.

Tisnaren is a freshwater lake fed by natural springs across the border between Östergötland and Södermanland, with water rich in nutrients that supports many fish species. The lake sits in a calm, wooded landscape with areas suitable for recreation and fishing.

The Tisnare Canal was built between 1910 and 1915 to simplify freight transport to the mainline railway station at Ändebol, on the Södermanland side of the border. The lake drains via Forsaån to Viren and is part of the Nyköpingsån river system. The Föreningen Rädda Tisnaren works to protect the lake and its adjoining waterways.

The area around the lake shows signs of settlement dating back to early times, with archaeological remains and carved markings visible in the surrounding woods. Visitors can observe these traces of past habitation while exploring the landscape.

The lake is accessible through natural boat ramps located in Skedevi and Hävla for easy water access. Fishing information and permits can be obtained from local sources in the towns of Vingåker and Katrineholm nearby.

Tisnaren drains through Forsaån to Lake Viren and belongs to the Nyköping River system. The Tisnare Canal, built between 1910 and 1915, was made to ease freight transport to the main-line railway station at Ändebol on the Södermanland side of the border. The lake's largest island, Tisenö, has a permanent population.