It is not atypical in the winter months for large chunks of ice to come floating down the river. Dams need to regulate the flow of water that is coming out of that dam. As a result of this the rising and lowering of the water height, combined with the changing of the temperature, will cause large chunks of ice to break off and float downstream. It’s a lot of fun to watch the icebergs float away and occasionally others partake too. While I was out the other day I enjoyed watching a Dipper perch on an iceberg and float away downstream before eventually flying off.