| Seven Island Lake Nature Reserve | |
| Alt Name: | Rezerwat przyrody Jezioro Siedmiu Wysp |
| Iucn Category: | IV |
| Location: | Warmian-Masurian Voivodeship, Poland |
| Coords: | 54.3°N 55°W |
| Area: | 10.06km2 |
| Established: | 1956 |
Seven Island Lake Nature Reserve (pl|Rezerwat przyrody Jezioro Siedmiu Wysp) is a nature reserve established in 1956 around Oświn Lake in north-eastern Poland, close to the border with the Kaliningrad Oblast of Russia.
The reserve is located within Warmian-Masurian Voivodeship, in Gmina Węgorzewo of Węgorzewo County.
The area is an important breeding ground for water birds, and is both a Natura 2000 EU Special Protection Area, and a Ramsar site − one of 13 such sites in Poland.
The reserve covers an area of approximately 10km2, consisting of about 3.5 km² of water bodies, 6 km² of marshland and 0.5 km² of forest.