Yes a blue heron or blue herons can swim.
Blue Herons are very good swimmers and can easily swim in deep water when needed.
Not only are blue herons good swimmers the blue heron can also do things such as hovering above the water before dropping feet first to pick it's prey off the surface of the water.
The blue herons diet consists of only fish that they can get from the water.
So when they are flying above the water the blue heron will hover above the water and once the blue heron sees the fish they drop down feet first and get the fish.
The blue heron may also go swimming when needed to get fish.