Identification Please

    We were out walking along the banks of the river Wear upstream from Durham city and watched this little bird for a while. It's quite small, maybe a bit bigger than a blackbird (hard to tell from 30m or so away. It dived often for up to 10-20 secs and once came up with a small fish to eat.   We're very curious as to what it is. Sorry, but the photo isn't very clear.