According to the manufacturers: “The product remains effective if the animal becomes wet. However, prolonged, intense exposure to water should be avoided. In cases of frequent water exposure the persistent efficacy may be reduced. In these cases do not retreat more frequently than once a week. If a dog requires a shampoo, it should be administered before applying Advantix or at least 2 weeks after application, to optimize efficacy of the product.” This information is also found on the information leaflet provided with the product.
In your case I would like to advise:
- Make sure your dog is completely dry at the time of the treatment
- Keep your dog dry on the day of the treatment and the day after so that the product will have a good chance to spread across the skin
- Treat every 3 weeks during the time when the dog swims frequently. Revert to once a month treatment once the swimming frequency goes down to once a week.
- Inspect your dog for tick and fleas once every week during grooming
Hope this can be helpful and keep up with the swimming as it is a very good exercise for Nellie!