The company has been moving the fish from West Smethwick Park in order to remove silt that has built up in the top lake.
New platforms for fishermen are also being installed as part of the scheme which is due to be completed in the autumn.
The enhancement works involve re-instating a stream that was previously covered over and installing fishing platforms, with disabled access, around the lake. The stream feeds into the lake via a pond and over the years the pond has filled up with silt.