🇩🇪 Kreidesee Hemmoor

The pit

Chalk was dug at Hemmoor from 1862 to 1976 to feed the cement works beside it. When the digging stopped and the pumps came off, groundwater filled the hole, and by 1982 there was a lake.

The original excavation went down about 130 m. Rubble from the demolished cement factory was tipped back into it, which brought it up to roughly 60 m — still the third-deepest body of water in northern Germany, in a country with no mountains to put deep lakes in.

What is in it

Thirty-three hectares of water taking about 35 000 dives a year, and the bottom has been furnished accordingly: vehicles, industrial machinery, the remains of the factory, and a Piper PA-28 that once belonged to the astronaut Alan Shepard. There is also an underwater postbox on the bottom, which is emptied weekly and the letters posted for real.

The other thing about Hemmoor

It kills people. Six divers died there between 2010 and 2016; between 2017 and 2022 there were fourteen accidents and four more deaths, with further fatalities in 2023 and 2025. The reasons are the usual ones for a deep, cold, clear inland lake: the visibility invites you down, the water is 4 °C at depth, and 60 m in fresh water with no decompression planning is fatal in exactly the way 60 m anywhere else is. Redundant gas is mandatory below a set depth.

The dives

Forty-one dives between August 2010 and November 2025 — the most of any site outside the Netherlands, and second only to 't Grasbroek overall. Deepest 43.8 m, longest 118 minutes. Fifteen years of going back to the same flooded chalk pit is what technical progression looks like when you live in the north of the Netherlands.

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Image: Hemmoor Kreidesee 01.jpg — User:Raboe001, CC BY-SA 2.5, via Wikimedia Commons.