Kotlářka retention basin, Retention basin in Prague, Czech Republic.

Kotlářka retention basin is a 0.6-hectare pond on the Motolský stream at its confluence with the Cibulecký stream, by Plzeňská street in Prague 5-Košíře. Built in 2016, it has a clay-sealed bed, banks and dam faced with stone, a stone-paved safety spillway, and a small bird island in its western part.

In the 1980s a dry flood-control polder called Homolka was built here on the Motolský stream, with a 108-metre earth dam 1.6 metres high and a capacity of 4,220 m³. Its absorption proved insufficient, and in 2016 Prague decided to replace it with a permanent pond. Construction required excavating up to 3 metres of historical building-waste fill, which enlarged the water surface and extended the open stream channel by almost 300 metres.

The area draws birdwatchers and nature observers who spend time watching waterfowl and other species that inhabit the water. Visitors often stop along the edges to observe and photograph the animals in their natural setting.

The site is accessible year-round and offers the best viewing conditions in early morning or late afternoon hours. Visitors should wear appropriate footwear since pathways around the water can be slippery after rain.

The central island provides a protected nesting ground that attracts different bird species depending on the season. This specialized habitat makes the basin an important refuge for waterfowl within the urban area.