The twelfth point of the Malcantone Mining Park Trail is the Bolle ponds.

The name of this locality Bolle means ponds. This area was one of the wetlands on the ridge of the Scerée hill. Unauthorised work carried out in the 1970s and the subsequent abandonment of the use of this area led to a return to the original wetland situation.

A wetland and aquatic flora has developed in this environment and various types of aquatic fauna in the ponds.

Ponds and wetlands are the richest environments for animal and plant species and therefore have a high biodiversity. Some of these species are even rare and endangered. To give a few examples, one can encounter the elegant dragonflies darting and chasing each other, or those strange animals that skate on water, the gerridae, specialised in catching the unfortunate insects that fall into the water and remain on the surface floating. Beetles, dipterans, water scorpions, shrimps, water spiders, some consume plant debris, others are predators of other animals. And of course, there are also mosquitoes. But don’t worry, in mature ponds, which have achieved a balance, there are enough predators in and out of the water to keep them under control. Tiger mosquitoes are not a problem. They lay their eggs in temporary and very small environments, such as small, abandoned containers, tyres…, where they manage to develop before they dry up. Under these conditions the predators that should control them cannot develop. Amphibians, frogs, tree frogs and toads, use ponds to reproduce. Here they lay their numerous eggs from which many tadpoles will hatch, which may be lucky enough to develop into adults. These animals are very sensitive to water pollution and find fewer and fewer environments suitable for them. That is why no store-bought goldfish or water turtles should be released in ponds: these animals also feed on eggs and tadpoles.

In lowland areas, wetlands are under pressure from human activities: land reclamation, pollutant inputs, and the release of competing and predatory species. More than 90 % of the wetlands once present in Switzerland have been destroyed. That is why those few that remain are environments that must be carefully preserved. They must be protected for nature but also for us.