A water body with 2.5m depth and 3000 square meters area is considered to be a pond or a lake?

From the wikianswers:

"Scientifically, a pond is any man made body of water where light is found in the entire pond body of water. A lake is any body of water that has a profundal-zone http://www.answers.com/topic/profundal-zone

Hence a water body of depth 2.5 m can at best be called as a pond only.

The nature of construction of the water body is given in the question. If it is a masonry/concrete construction it can be called a as sump/tank/reservoir as well.

Usually ponds and lakes have natural ground as the base.

Gopalakrishnan.P