Saturday about noon and we headed out for a drive. Before we even got out of town it started to rain. But we carried on and headed for Collingwood, intent on finding some pots of spring flowers. Eventually, we were successful.
Looking closely, it appeared that the waves from the bay were washing in and bumping into the current coming down the river, creating a boiling, churning upwelling in the river. Presumably the river was churning up the insects, attracting the swallows. Fascinating!