Lake Aasee remains safe bathing water: water quality remains good

Although the Bocholt bathing bay will probably remain closed for a few more days due to ongoing work to restore the subsoil, the administration emphasises that this has nothing to do with the water quality. The latest measurements also show that it is still good.

The downgrading of Lake Aa from "excellent" to "good" in May does not relate to the water quality, but to the assessment as bathing water by the state Ministry of the Environment. The water quality itself is still good, as current measurements show. The background to this is previous closures of Lake Aa due to blue-green algae, which led to the automatic downgrading - not new measurement results or a deterioration in water quality.

The regularly analysed parameters, including contamination with bacteria such as Escherichia coli and intestinal enterococci, show no significant changes. In the current year 2025, the values remain at the same level as in previous years.

The water quality is checked by taking monthly samples at three defined points in the lake. These are carried out under defined conditions with subsequent laboratory analyses, the results of which are available a few days after sampling. The most recent samples also show no abnormalities in the measured values.

The city of Bocholt helps to stabilise the water quality with three Aquamotec systems, among other things. These ensure an improved oxygen supply by circulating and aerating the deep water, which supports the natural decomposition of sludge and promotes the ecological balance, especially in hot summers. In addition to its importance as bathing water, the Aasee also serves as an important local recreation area, habitat for flora and fauna and as a technical flood buffer, for example after heavy rainfall events.

The city of Bocholt often receives proposals to channel water from the Aa into the Aasee to improve the water quality. However, even external water experts cannot confirm a positive effect on the water quality. On the contrary: experts warn of a possible additional nutrient input, which could, for example, favour the formation of algae.

Critical water quality is difficult to recognise without sampling. Visible blue-green algae infestation can be indicated by greenish or bluish haze and creaming. Other contaminants such as bacterial contamination, on the other hand, are not visually recognisable. Regular, standardised measurements are therefore essential.

Further information on water quality and the measured values can be found on the website of the State Agency for Nature, Environment and Consumer Protection (LANUV) and in the bathing water profile of Lake Aa.

Release for bathers

Remaining work to remove the deposits in the bathing bay is still ongoing. This could not be fully completed this week. Following consultation with the company commissioned, the administration expects to be able to reopen the bathing bay for bathing next week.