Styggforsen is a waterfall and a nature reserve located in Dalarna County, Sweden. It is part of the European Union-wide Natura 2000 network.

The waterfall is located in the village of Boda, 20 kilometres north of Rättvik. It lies at the eastern edge of the Siljan Ring, a prehistoric impact crater formed 377 million years ago during the Devonian period. This crater was created when a bolide, estimated to be about 4 kilometres in diameter and traveling at around 100,000 kilometres per hour, struck the Earth's surface. The impact caused a significant vertical realignment of the horizontal rock strata and created a bedrock depression, resulting in many of the geological features present today, such as Lake Siljan to the southwest and Styggforsen itself.

The Styggforsån river is interrupted by the 36-meter-high Styggforsen waterfall, which is composed of a column of Ordovician limestone. The waterfall's base meets a dike of brecciated quartz believed to predate the impact event. This site is popular with tourists and features a circular path about one kilometre long that leads to a cave called Troll Hole. During the summer, a cafe is open, and there is an information centre nearby.

In 1979, a nature reserve of approximately 12 hectares was established around the waterfall, and in 2005, it was incorporated into the Natura 2000 network. The area's moist climate supports a diverse range of lichens, mosses, and plants, including the rare orchid Epipactis atrorubens, Additionally, it provides a habitat for many insect species, including Venusia cambrica, Hyloicus pinastri, and Epirrhoe alternata. Within the nature reserve, picking flowers and any activities that could affect the environment are strictly prohibited.

Ingmar Bergman's film, The Virgin Spring, used Styggforsen as one of its locations.