Just a warning, there are people very much in favor of the swim with the dolphins by Vallarta Adventures and those very much opposed. The choice, of course, is yours. One alternative you may consider is the Dolphin Encounter through Open Air Expeditions.
When the whales are in the bay, you can combine Dolphins and Whales. When the whales leave it reverts to the Dolphin Encounter.
Half day trip (5 hr), small boat with professional guides go into the bay and find groups of dolphins, where if conditions are right, you can join them in the water. These are wild dolphins and completely free and if they choose to interact with you in the water, it is their choice. Naturalist and Hydrophones on board, 525 pesos per person, 315 pesos under 10 years old. Includes continental breakfast, lunch on the beach, soft drinks and snorkeling gear. You can find out more about both encounters if you click on the top banner link,\"
What to Do\".
Which ever you choose, have a great time.