Yellow-bellied slider

Description:

Adult male yellow-bellied sliders typically reach 5–8 inches (13–20 cm) in length; females are anywhere from 8–13 inches (20–33 cm).[4] The carapace (upper shell) is typically brown and black, often with yellow stripes. The skin is olive green with prominent patches of yellow down the neck and legs. As the name implies, the plastron (bottom shell) is mostly yellow with green spots along the edges. Adult males tend to grow darker as they age.

Habitat:

The yellow-bellied slider (Trachemys scripta scripta) is a land and water turtle belonging to the family Emydidae. This subspecies of pond slider is native to the southeastern United States, specifically from Florida to southeastern Virginia, and is the most common turtle species in its range. It is found in a wide variety of habitats, including slow-moving rivers, floodplain swamps, marshes, seasonal wetlands, and permanent ponds. Yellow-bellied sliders are popular as pets.

Notes:

The fact that they are pets may explain why they can be found in ponds here in Europe. probably some people released them and they breed in the ponds since then.