In summer (November–April) Seal Swim Kaikoura run trips that allow you to swim with fur seals.
You have the option of either a shore-based or boat-based activity, which means that you can either snorkel out to the seals from the beach or take a boat out to see the seals. The boat-based tours are the most popular as these have the highest success rate of being able to swim with seals.
The trips involve around an hour in the water swimming with seals, although you should allow 2½ hours for the trip.