A massive environmental monitoring station off Germany's Baltic coast has disappeared from the seabed, baffling police and researchers.
The seabed "observatory", worth about €300,000 (£270,000), weighed more than half a tonne. It could not have been dragged off by a storm, tide or large animal, German experts say.
Divers only found a torn power cable at the site, 22m (72ft) down and 1.8km (1.2 miles) offshore.
It is a prohibited area, north of Kiel.
No boats - not even local fishing boats - are allowed into the area, called Eckernförde Bay, about 70km (44 miles) south of the Danish border.
The missing observatory, installed in late 2016, stopped sending data on 21 August.
It consisted of a power unit, connected by cable to the coast, and an instrument unit, which together weighed 770kg (1,700 pounds).
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The German instruments had been measuring seawater quality, including temperature and the levels of salt, oxygen, nutrients, chlorophyll and methane.
"The data we get from it is priceless," said Prof Hermann Bange, head of oceanographic research at Geomar, a scientific centre in Kiel.
Geomar has appealed for any witnesses who might have spotted suspicious activity in the area on 21 August. "Or maybe someone will find parts of the apparatus somewhere on the beach," he said, in a Geomar statement (in German).