I have been researching this for quite awhile for the lake I live on

a shallow at most 25 foot 14 acre lake.

1 - you have to have some type of plant life
2 - water fleas and or water daphnae live on the plants in the shade of the plant

3 - fry eat the daphnae

4 - bigger fish eat the fry

you can put all the fish you want into a pond and it wont mean a thing without plants

the plants also absorb the extra nitrogen from the fish poop
and
they block the sun and that keeps the algae down.

A great pond plant are impatients - mine are over 2 feet tall now - i put them right into the water

Pity for the guilty is treason to the innocent