Grebe? Diver?

I followed this lovely bird along the canal on my way home - he appears on the water and then dives down.....  I wait, and wait, and then he reappears far further along than I thought he would.  So I jogged along the towpath trying to guess where he would pop up again.  
I thought originally it was a grebe, but can't match an image online.  I'm sure someone will enlighten me.