Birds: North American Tern?

I was watching these birds above a pond near where I live in Utah. They were grey/white on the bodies and had a grey head. They were just smaller then a common seagull, but they were shaped like what I believe to be a Tern (a swallow, except thinner wings and longer, two point tails). They would hoover above the pond for a bit then pull in their wings and dive into the water and come out almost five seconds later. They made a shrill clicking sound. Does ANYONE know what particular type of bird this might've been?

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