Swimming with dolphins can alleviate depression. Seriously. A group of researchers in Honduras got patients suffering from clinical depression and divided them into two groups. One bunch went snorkeling on a nice tropical beach (which Honduras has a good supply of). The other group did the same, but with dolphins.
Not surprisingly, both groups saw a reduction in the severity of their symptoms, but the dolphin group saw a significantly greater reduction. In other words, dolphins make you happy, even more than snorkeling does.
This result is similar to findings in past studies involving domestic animals like dogs and cats. We're social animals, and even having a nonhuman animal around is better than being alone. Moreover, we do tend to pick up mood cues from those around us -- if you're in a crowd of happy people, you get happier. Apparently being around dolphins (famous for being relentlessly cheerful animals) does the same.
This also suggests that sad people who live inland should invest in very large bathtubs and find some Web site offering next-day cetacean delivery.