At the beginning of May, a measuring device was immersed at the northern end of the lake. Two more are to follow after a test phase in the south and the middle of the lake. "The system warns of persistent oxygen deficiency in the water and above the sediment at the bottom of the lake," the city said. As a countermeasure, the water could then be circulated with pumps. Lack of oxygen in the water is considered a trigger for botulism, which was proven to be the cause of death in waterfowl in the Rheinaue lake in 2018.

To improve the situation in the Rheinaue lake, the city had already initiated other projects - with some success - in the past two years. Daisies were planted at the waterside to regulate the population of waterfowl, reducing the amount of excrement. The plants are unattractive for waterfowl, designed to displace them. As well, geese prefer short green grass and easy access to the water so mowing is now less frequent, allowing the grass to grow long. A feeding ban for water birds and nutria has also been in force since 2019. The water in the lake is also permanently renewed, with cooling water from the Post Tower being fed into and drained into the Rhine. The algae growth in the lake was removed three times with the help of mowing boats.

In the spring of 2019, the city commissioned a specialized bureau to draw up a redevelopment concept based on the results of studies. For this purpose, measurements were taken between March and September 2019 for various factors, including water temperature, oxygen and phosphorus content. According to the study, the high phosphorus content is the main reason for the poor water quality. On the one hand, this is caused by the sediment which releases phosphorus, on the other hand by the tributaries which have a high phosphorus content. " For this reason, further studies were commissioned for the tributaries, so that possible measures to reduce the phosphorus content could be defined.

In addition to aeration equipment, the experts recommend the use of ultrasound to combat blue-green algae (cyanobacteria). The necessary preliminary investigations are to be commissioned in May. In the experts' opinion, sand fleece should also be laid in the lake's edge areas to reduce the release of phosphorus from the sediment. For the year 2021, the experts recommend complete removal of silt from the lake. Depending on the pollutant content of the sludge, remediation would cost between 3.76 million and 4.22 million euros. The funds have been submitted for the 2021/22 budget.