Definition of water levels:
(n) :
The level of a body of water, especially when measured above a datum line.
(n) :
The level of the water table below ground.
(n) :
The waterline of a ship.
(n) :
(also attributive) (Relating to) an instrument to show the level by means of the surface of water in a trough, or in upright tubes connected by a pipe.
(n) :
(attributive) Of a route that follows a riverbank or shoreline.