Oset, Nature reserve in Örebro Municipality, Sweden.

Oset is a nature reserve in Örebro Municipality featuring wetlands, forests, and open areas near Lake Hjälmaren. The mix of different habitats creates space for many plant and animal species throughout this landscape.

The area was shaped by the lowering of Lake Hjälmaren between 1878 and 1887, which created its shore forests, wet meadows and reeds. Ornithologist Erik Rosenberg discovered its birdlife and pushed for a hunting ban in the inner part of Hemfjärden. Örebro city council made it a nature park in 1943, and in 1968 the nature reserve was established; it was enlarged in 1986 and 2002.

The reserve has three rest houses, including the Erik Rosenberg cottage, where visitors can stop and learn about the natural environment. These spots help people understand the landscape and the creatures that live there.

Walking paths and information boards guide visitors through the reserve and make exploring straightforward. The area is also laid out to be accessible for people with limited mobility.

The wetlands here are protected under the Ramsar Convention and matter greatly to birds that migrate across many countries. The site plays an important role in international bird migration routes.