Tips for setting up a pond to prevent pests from eating the fish.
Make Hiding Places
When you make your pond, be sure to construct some hiding places at several water depths for your fish like a rock condo, rock overhangs and use plenty of pond plants. That way the fish can hide when they sense danger. Also, try not to leave too many flat ledges around the pond for pets or other animals to use as fishing spots.
My sis-in-law, in California uses inexpensive lattice to keep unwanted raccoons and other predators from her fish pond. Just place them over the pond in the early evening, EVERY evening. Works like a charm.
If you are planning to have Koi, carp or goldfish in your pond and you live in a very rural area filled with lots of critters remember to invest in some fine leaf netting. Draping this netting over your pond at night can prevent night creatures from making a meal of your precious fits.
Netting And Water Hyacinth
In our small pond, there is a problem with big herring birds - legs like stork. They will eat all the fish they can catch! Put a frame over the pond, if not too large, and attach plastic netting. Add some water hyacinth (they multiply very fast, so you don't need many). It is an aquatic plant with blue flowers: a perennial aquatic plant, native to the subtropical Americas but also found elsewhere that has glossy rounded leaves with bulbous stalks, and lilac-blue flowers.
Widely cultivated as an ornamental, it has become a troublesome weed of waterways in many subtropical regions, including Australia, Africa, and Southeast Asia.
Watch Out For Water Hyacinth
Regarding the water hyacinth. Syd is right. Here in Australia it's a noxious weed, and a 'banned' plant as it takes over so quickly choking creeks and waterways. It's beautiful to look at, but bad in habit. Seems like it's not yet classified as a noxious weed in America and Canada.
My daughter has a pond with fish in her front garden, she doesnt have a 'net' over it but does have lots of 'hidey holes' for the fish among the rocks and water plants. Her cat laps from the pond, but doesnt attempt to catch the fish, and the dog is around the back behind the gate. I guess 'fishing' birds could be a problem, but she hasn't lost any fish yet.
Advice On Depth, Mosquitoes And Plants
The local gardens in our city just make certain the ponds are at least three feet deep and have plantings all around the edges. Koi are WAY too expensive to purchase and not know everything about them. I'd suggest regular goldfish if your pond is going to have a solid bottom. If built in a wet area with a dirt bottom, most ANY kind of fish will survive if it's deep enough and has circulation.
Remember to add the Mosquito Wafers every few months, sort of at the same time as furnace filters. I believe they claim not to harm fish, but read first. If you are in a cold climate, the pond should be heated somehow, and deeper and covered often.
The water lilies need a pond all to themselves. Hyacinths are lovely but not welcome anywhere anymore. Horsetail herbs are quite nice and distinctive, along with water irises. I have a 3'x 3 1/2" "bog",or also known as a "tub garden", with a bonsai Cypress tree growing among dwarf cattail reeds and water iris. Whatever you do, do not allow what I think is called Duck Cabbage to get started. It overgrows and quickly takes over, as do some Mallows. Read carefully before adding water plants and fancy fish.I have had mosquito-eating fish like the ones Israel has now added to their citiy fountains, but the winter got so cold one year they all died out. I hope the formula I've just discovered on the Internet will work to prevent mosquitoes from living there. Good luck and God bless you.