where do bugs come from in ponds?

Most are larvae from flying insects or beetles that breed in water where they deposit eggs.

Science is still inconclusive how a small lake well isolated from rivers, creeks or springs has an abundance of fish.

They didn't fly, they didn't crawl, highly unlikely human stocked, but they are there, breeding and surviving just fine.

Speculation a predator bird snatched a fish, and dropped into the lake and just happened to survive and also happened to be a gravid female.

Water skeeters can fly as adults, but they mate, breed, lay eggs in water like mosquitoes do.

Difference is the skeeters practically never migrate or leave their water habitat unless driven out.

The adults fly there and lay eggs, which then hatch into aquatic larvae. Some bugs however never leave the pond, if the pond never dries up. Even if a pond dries, the bugs can still lay eggs which survives in the mud until the next rains or floods come.

The adults fly.

Warning: do NOT pick up a backswimmer with your bare hands to look at its wings.

They fly

Sudden increases in salt concentration in the water of gerrid habitats can trigger migration of water striders. Water striders will move to areas of lower salt concentration, resulting in the mix of genes within brackish and freshwater bodies. Nymphal population density also affects the dispersal of water striders.

The higher density of water striders in the nymphal stage results in a higher percentage of brachypterous adults developing flight muscles. These flight muscles allow for the water striders to fly to neighboring bodies of water and mate, resulting in the spread of genes.

Birds feet bring in the eggs....

Eggs. Just like where you came from (except for the pond)

Eggs that ( I think) float on the surface then awayyy they go!