What is this bird?

It was sunny this morning after the mist had lifted so we went to the Creek Hide to see if we could get a view of the Water Rail. No luck - only the moorhen were on show. On the way back to the car we stopped off at the Curlew Hide - there were a couple of little egrets about but not close in. Then we saw this bird swimming near the opposite bank. It behaved like a cormorant - diving and presumably fishing. Open to suggestions as to what the bird is:

 

Richard D tells me that this is a juvenile Great Crested Grebe. Apparently this is unusual for the Teifi at this time of the year.