No matter what type of fish you stock in your backyard pond, predators ranging from housecats to herons could injure or kill your prized pets. Starting out with a pool designed for fish safety helps, but even poorly designed ponds benefit from added shelters. Since predators attack from above as well as from the banks and shallows, the best solution shelters the entire pond with permanent netting.
Aquatic plants offer fish natural cover. Place container-grown plants in deeper water to keep the shelter out of reach of animals and birds that hunt from the banks of ponds. Floating vegetation like water lilies provides shade, adds beauty to the pool and screens the fish from the view of overflying predatory birds.
Short sections of large-diameter black plastic pipes give fish excellent hiding places. Lay the pipes in deep water away from the shore, and choose diameters large enough to give even the largest fish in the pool safe passage. Ready-made quonset-style fish shelters of wire mesh or plastic work equally well.
Woven wire fencing shaped into half-round or box shelters allows small fish to enter but keeps predators out. Fish swim directly through the lattice of the fencing, out of reach of animals and birds.
The cut tops of small bushes or trees sunk to the bottom of a pool offer cheap but temporary shelter, since the wood lasts only a season or two. Debris could cause problems with circulating pumps and filters as the wood decays, however.
Nets and Fences
For full protection, shelter the pond itself rather than just the fish. Hawks, gulls, herons and shorebirds all may find the pond an attractive feeding spot. Netting stretched over the pond on a permanent frame keeps out predators with a variety of habits. Parallel wires or strands of fishing line strung over the pond discourage birds from landing on the water. Parallel strands on posts around the shore perimeter prevent large wading birds like herons from approaching by land. Strand barriers don't always offer permanent solutions. If one bird finds a way through, others will follow.
Building shelter into the pond offers a variety of protection for pet fish. Structures overhanging the banks give shore-hugging fish extra places to hide, but provide hunting perches for shorebirds unless raised well above the water level. Deep water and steep banks keep raccoons out of the feeding zone. Water over 18 inches deep also discourages wading birds. Larger fish like koi need at least 4 feet of water depth, and deeper ponds provide much better protection from both predators and weather extremes.