The Limnoplan specialist office for water and fish ecology took care of fishing and relocating the fish. The biologists caught around 1,000 fish from the eastern half of the lake alone, including carp weighing up to 40 kilos. River perch, sunfish and tench dominate among the nine species of fish recorded, accounting for around 80 percent of the individual fish counted. However, other species such as pike, bream and carp also occur.

Carp were caught and transferred to other waters because they would otherwise eat away at the planned new planting in the Rheinauensee. Invasive species such as the sunfish and the marble goby were also found in the Rheinauensee.

In accordance with the EU directive on combating invasive species, these fish were removed from the lake because they would otherwise continue to displace native species and cause damage to the restored lake.

The sludge was pushed together using machines. Due to the high organic content, the disposal costs for the sludge are very high. To minimize these costs, the mass was separated into grain sizes using various sieves. Once cleaned, the coarser stones can be reused later and thus disposed of more cheaply. The remaining fines were dewatered using centrifuges. This meant that significantly less material had to be removed and disposed of.

Sand was then applied to the bottom of the cleaned lake. The 15-centimetre-thick layer serves as a substrate for the newly planted macroalgae and as a habitat for microorganisms. A sand fleece replaces the sand at the overflows and outlets to prevent it from being washed away.

Following the example of the Phoenix Lake in Dortmund, the refilled Rheinauensee was planted with macroalgae. Macroalgae bind phosphate and thus minimize the growth of other algae.

The bank wall was also renovated. Exit aids for water birds were also built in the same stone as the wall. The restoration of the bank areas was funded with around 175,000 euros via the NRW state monument funding program.

The restoration concept for the Rheinauensee pursued three objectives: Firstly, the appearance of the lake was to be significantly improved from a landscape aesthetic point of view by reducing the growth of algae. This would also improve the usability of the lake for the local boat rental company. And an ecologically stable body of water without animal mortality should be created.

Citizens can also make a decisive contribution to this by not feeding the wild animals!

Around a year after the successful restoration of the Rheinauensee was completed, the Office for the Environment and Urban Greenery had additional fish introduced into the water in December 2023. This will gradually increase the diversity of species and establish a stable community in the 15-hectare lake.

Tench, roach, rudd and gudgeon with a total weight of 200 kilograms were added in various sizes. The macroalgae planted after the restoration have spread well and serve as a nursery and habitat for the new lake inhabitants. Countless microorganisms, such as insect larvae, have also been able to develop in the water so that the fish can find sufficient food.

In 2024, further species will be introduced in several stages. These will include small fish such as the bitterling. The latter depends on the pond mussel, which is found in the lake, to reproduce and lay its eggs in its gill cavity. The mussels in turn benefit from the fish, as their larvae attach themselves to the fish and are thus spread. Finally, predatory fish are introduced into the lake. These ensure a balanced species composition and thus a balance in the lake.

Even if many people think they are doing something good for the animals when they feed them: Inappropriate food is unhealthy for wild animals and not in the interests of animal welfare! The animals reproduce too much and there is no natural selection, as is usually the case with wild animals. In addition to food scraps, an excessive amount of animal excrement ends up in the water and can no longer be broken down naturally.

This leads to an increased phosphate input and thus to an excess of nutrients in the water. At high temperatures, algae multiply particularly quickly as a result. It can also lead to a lack of oxygen in the water, causing bacteria to produce toxins. Waterfowl and fish can quickly die as a result.