It is ideal for a pond to be rectangular, because this makes it easy to maintain, especially when guarding it against silting. It is also easy to harvest fish from a rectangular pond than from a pond of any other shape because you can easily sweep through all the corners.
If several ponds are constructed, they should be parallel to each other to ease management. Make sure that each pond has got an inlet and outlet.
Some are constructed with the wrong depth. Some have no proper water outlets and inlets and lack the recommended gradients.
Fish cannot survive under such conditions.