Waterholes, rainwater basins and watercourses
The city’s blue areas are often made up of small ponds in the gardens or parks or by the city’s river basins.
Ponds can easily swarm with life. It is especially possible to see large amounts of water insects such as the very beautiful and striking dragonflies, where both the eggs and caterpillars live in water. The city’s waterholes are also valuable breeding areas for frogs and water salamanders.
Moreover, the water areas are habitat for many water plants. The spreading of these is, however, a very slow process in the cities, which means that it can take several years to achieve merely a decent species rich flora in the city’s waterholes. It is easier with water animals, which spread over large distances by the wind! Fully-grown water ticks, water beetles and dragonflies fly far around to look for waterholes. It is also possible to see great diving beetles, which actually land on cars because they think their roofs are shiny surfaces of water.
However, the biodiversity in the city’s blue areas will decrease dramatically if goldfish or carps are released. These larger fish cause heavy manuring of the water through their activities. Together with duck feeding, the release of fish is the biggest threat against biodiversity in waterholes. Both factors add large amounts of nutrients, which allows algae to grow and this makes the water murky.