Top up ponds and water features if necessary - a spray attachment on the hose will aerate the water, and help the fish.
Any pumps on water features should be left on during sultry nights, as oxygen levels are lower in such conditions.
Remove dead foliage and blooms from waterlilies and other aquatic plants. Cut back any marginal plants that are getting out of hand. Continue to skim blanket and floating weeds.
Cover ponds with nets or safety grills in gardens where young children play. These have the additional advantage of preventing leaves falling into the pond.
Clean out debris lurking in the depths of the pond. This will improve the water quality and prevent excess debris from promoting the growth of weeds, algae or marginal plantings, and from releasing toxins that could harm fish or wildlife.