There are some steps you can take to reduce the risk of spreading unwanted plants and disease:
First - consider whether you really need to visit a site you know to be affected.
Second - be hygienic. Clean your footwear and equipment between ponds, even if you haven't seen any signs of disease or invasive plants.
Drying equipment out is enough for some plants and diseases, but a mild bleach solution will help (make sure the bleach doesn't end up in the pond!). If you regularly use a pond for pond dipping where an invasive plant or disease is present, it may be sensible to have a set of equipment that is only used for that pond, and use 'clean' equipment for other ponds.
