Swimming with dolphins can cure mild to moderate depression, claims a new study.
Researchers from the University of Leicester studied the effect of swimming and snorkelling with dolphins on 15 people with depression in Honduras.
The researchers found the group's symptoms improved compared to another group who swam in the same area, but not with dolphins.
The team assessed the anxiety levels before and after the group's daily swim with the dolphins by measuring the levels of a stress indicator known as cortisol in their saliva.
They also measured the levels of endorphins, which promote calm.
After swimming with the creatures, the researchers saw lower cortisol levels and higher endorphin levels in the participants.
"Depressive symptoms improved after two weeks of treatment. In conventional therapy - psychotherapy or drug therapy - symptoms usually improve substantially after four weeks," wrote the researchers.
Volunteers taking part did not take antidepressants or have psychotherapy a month before the trial so that the researchers could see the full effects the dolphins had on the group's depression.
The findings of the study, published in this week's British Medical Journal (BMJ), supports the theory of biophilia, which says wellbeing is linked to our relationship with nature.
It is thought the calming environment, the warm water and the texture of the dolphin's skin has a positive effect on people who have contact with them.
The authors concluded: "Animal facilitated therapy with dolphins is more effective than water therapy in treating people with mild to moderate depression.
"Despite some study limitations, the effects exerted by the animals were significantly greater than those of just the natural setting."