If your water garden contains tropical plants or other plants that won't survive the winter, toss them into the compost pile. If you have fish, stop feeding them about the time you remove the plants: fish don't swim as much in the winter and their metabolism slows, so they don't require any food until early spring.
Leaves and Scum
In the fall, prevent leaves from entering your pond by placing plastic netting across the pond's surface or by regularly using a rake to remove the leaves. If the leaves make it to the bottom, they'll slowly decay and release toxins that can kill the fish and upset the ecological balance of the pond.
To remove pond scum, draw a sheet of newspaper across the water's surface. About every week or so, remove the top filter from the pond and clean it with a high-pressure spray from the hose, then replace it so the pump is not forced to work any harder than necessary.
Fish and Algae
If you live in a climate with very cold winters, fish will survive in a pond even if the pond forms ice a foot thick, assuming the pond is at least two or three feet deep. To prevent overall freezing, toss a rubber ball or a piece of wood into the pond. When ice forms, push down on the ball or wood to crack the ice and admit oxygen to the shallow layer of air beneath the ice.
Algae serve as a source of food for fish but often cause problems for water gardens. Too much algae can make the water become murky and deprive fish of oxygen. Algae don't pose much of a problem during the summer and fall because the pond is typically full of plants that prevent algae from growing and shade the pond from the sun.
A copper-based herbicide will kill the algae without harming the fish, but you can also use a brush to gently remove algae from rocks and the pond liner. Another method of combating algae is to introduce snails and tadpoles to the pond, both of which will eat the algae.
Leaks
If a slow leak is discovered, try to determine its source. Inspect the liner for any visible holes and make sure it hasn't been pushed down by the weight of rocks on the top edge. To repair such a problem, take a spare piece of liner and place it over the original liner, then mound up and pack down the soil. The weight of the water should hold the new liner material in place (use rubber cement for additional security).
