Lake Tegel, Recreational lake in Reinickendorf, Germany.

Lake Tegel is a large water body in Berlin's Reinickendorf district, surrounded by parks and residential areas with several small islands within its waters. The lake connects to the Havel River and forms an important part of Berlin's waterway network.

The name Tegel was first recorded in 1322 as Tygel, referring to the wider territory rather than the lake itself. The lake forms a branched, five-kilometre-long extension of the Havel and is administered as part of the Havel-Oder-Wasserstraße. On 25 March 1852 the Vincke–Bismarck duel took place on its shore.

The name Tegel comes from a Slavic root meaning "appendage", fitting a lake that is an offshoot of the Havel. The Greenwichpromenade on the northeast shore is laid out as a long tree-lined promenade with benches and playgrounds, ending at the Tegeler Hafenbrücke, known as the Sechserbrücke. On 25 March 1852 the Vincke–Bismarck duel was fought on the lake shore.

The lakeshore is easily accessible by public transport with multiple entry points along the water's edge for visitors. Water conditions and seasons should be considered, as the lake is cold in winter and recreational use may be limited during colder months.

On 25 March 1852 the duel between Vincke and Bismarck took place on the lake shore. The lake reaches its greatest depth of just under 16 metres between the Reiherwerder and Gänsewerder peninsulas. In June 2017, 14 dogs died within days after a poisoning; an autopsy found a rare toxic blue-green alga in at least one case.