82 Vette will not start

Just installed new water pump. Engine started but check engine light appeared. Has never done that before. Mechanic disconnected battery and reconnected. Now engine will not catch. Engine is flooding. What can be wrong? Thanks for your help.

If the engine is flooding either the fuel pressure is too high (unlikely) or there is a carburetor problem.

Since the car likely has a stock Quadrajet on it, flooding can be caused by:
Float level too high.
Float needle not sealing.
Float gas logged and sinking.
Jet well plugs leaking like a sieve.
Choke flap stuck closed and/or choke pull off diaphragm faulty.

This is all assuming there really is a flooded, meaning too much gas, condition.
An '82 is bone simple to service. This should not be too difficult to figure out.

You might check the engine oil. If the oil smells of gasoline then it should be changed.
If the flooding has been severe and chronic enough, excess gasoline can wash down the cylinder walls and prevent an engine from starting. If this is the case, removing the spark plugs and squirting a small amount of oil in each cylinder followed by reinstalling the plugs should help this problem; once the cause of the flooding is fixed. Hope that helps.