Dear Glug,
Homes need cleaning and so do ponds. The janitor of a pond is the common crayfish. The crayfish is the largest invertebrate in the pond. It is easy to obtain them; however you need to be cautious.
You can get crayfish by trapping them in local streams or hand collect them. Or you can buy them. Many seafood markets will sell local crayfish for boils. There is a problem however; if you bring crayfish to the pond, many of them will leave immediately. Often gravid females will stay and many males will move. You must restock repeatedly to get a good population. If you improve their habitat, they will stay.
Be very careful in obtaining crayfish. Many ornamental species are foreign to your environment and some are very invasive in the natural environment. Since they walk around, it is easy to introduce an invasive species. So check with the local government fishery people to determine what kind you want.
Once you get a population of crayfish, they will be self-sustaining (600 million year old survivor). They not only clean the pond but also are a top bottom predator (built like a tank). There are many top predators of varying size. Top predators are extremely important in the pond. The largest insect larvae in the pond are dragonfly that will bite you. Everything eats everything else smaller than itself (a rainbow trout will eat fish half its size).
Glug, I know crayfish threaten your eggs; however, you must keep checking over your shoulder. Everyone needs to be wary in this life. I know your house needs big and small fish; turtles and even birds. I want you cautious and knowing each of the inhabitants makes your environment healthy. The killers are important; they eat the weak and dead.
PonDoc from the pond