While I want this to be true, I am decidedly skeptical on the whole thing. Besides the fact there have been no sightings in over ten years, this decidedly lower quality photo isn't very telling, and the color is also quite unusual. I don't believe its a porpoise, they are a notably different grey color, and also have a VERY low profile when they surface. Yet still, I'm not convinced its a dolphin either, as they were also more of a light grey color, as opposed to pink.
Honestly, I think it might just be a large dead catfish that got carried up to the surface for a second, but that's just me.