Diemeltalsperre Strandbad Helminghausen

Germany Lake 1 - Excellent

Diemeltalsperre is a reservoir in the Waldeck-Frankenberg district of Hesse, created in 1924 by damming the Diemel and Itter rivers. The reservoir extends over 7 kilometres and covers 165 hectares, reaching maximum depths of 34 metres. It is surrounded by forested mountains of the Sauerland and lies within a nature reserve of the same name. The water body supports navigation on the Weser during low water levels, flood control, and hydroelectric power generation.

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Water

Reservoir (Talsperre) with a capacity of approximately 20 million cubic metres when fully filled. Surface area of 165 hectares. Maximum depth of 34 metres. Mean depth of 6.43 metres. Elevation of 375 metres above sea level. Water levels fluctuate seasonally: lowest in late summer, highest in spring.

Location

Helminghausen district of Diemelsee municipality, Waldeck-Frankenberg county, near the Hesse-North Rhine-Westphalia border. Parking, gastronomy, campground, and lawn areas are available. The beach is located on the northern shore of Itterbucht.

Facilities

Parking, gastronomy, campground, lawn areas, public toilets. The beach is 100 metres long and predominantly covered with gravel.

Season

1 June 2026 to 16 August 2026.

Water Quality

Classified as excellent quality for 2021–2025. Monitoring shows Enterococci and Escherichia coli levels consistently below or near detection limits (<15 KBE/100ml). The reservoir has elevated nutrient loading (mesotrophic classification, trophic class 2) but no management measures are required for hygiene. Potential pollution sources include municipal wastewater, combined sewer, and stormwater discharges. Low risk of future cyanobacterial blooms and low observed occurrence during bathing season.

Risks

Potential hygiene risk from municipal wastewater, combined sewer, and stormwater discharges into the lake. Risk of cyanobacterial blooms classified as low. Water level fluctuations affect beach location.