Water castle

A water castle is a castle or stately home whose site is entirely surrounded by water-filled moats (moated castles) or natural waterbodies such as island castles in a river or offshore.

Topographically water castles are a type of lowland castle. The term is mainly found in European-language sources, e.g. under its German names of German: Wasserburg or Wasserschloss, but is also used in English-language sources, usually those referring to European castles of this type. Forde-Johnston describes it as "a castle in which water plays a prominent part in the defences..."

There is a further distinction between:

In all cases, water is used as an obstacle to hinder an attacker. That apart, an abundant supply of water was also an advantage during a siege. Such a castle usually had only one entrance, which was via a drawbridge and that could be raised for protection in the event of an attack. To some extent these water castles had a fortress-like character.

In many places in Central Europe castles that had formerly been fortified changed their role or were converted over the course of time so that they became largely representational and residential buildings. The characteristic moats thus lost their original security function, but were retained in some cases as an element of landscaping. Today, in monument conservation circles, they are often described as burdensome, cost-intensive "historic legacies" because of the water damage caused to their foundations. As a result, many moats around castles in Germany have been drained, or more rarely filled, especially since the 1960s.

...
Wikipedia