Abstract: An underwater anchor for keeping floating structures in position in oceans or other waters has at least one oblong cylindrical hollow body constructed in such a manner that it can withstand the external water pressure at the depth at which it is used. The body has a positive floating power when its interior is almost entirely filled with air. One or more fastening points for anchor cables are located on the body and it may have one or more connections for adding ballast to the interior of the body.