I watched these two for about 2 hours last night at Cattus Island County Park.
The egret had the heron penned in behind a small sedge in the marsh and wouldn't allow him to pass into the pond he had claimed as his fishing ground. Every time the heron would attempt to enter the egret's territory, the egret would force him back behind the sedge. Then while the egret's attention was elsewhere the heron snuck by and quickly grabbed a fish and then the chase ensued.
This time being quick and sneaky was better than being big and the heron escaped with his fish.