Which is better for weight loss, swimming or running?

i recently started gym to lose some weight due to a wedding in about 3 months, so the gym i go to also has a swimming pool and was wondering which is better for losing weight. the thing is i love swimming and usually swim for about 80 minutes, and when i use the tread mill i run for like 30 mins and get tired then about 30 mins later i run for another 10 mins. so does anybody have any idea of which is better to shed some weight. thanks