In the swimming area, there are around 10 to 15 tall posts in the water. They have white caps on the top. What are they for?

Thank you!! I would have never known

To present obstacles for the rowing clubs during regattas. But really, was there last weekend and didn't see a use for them except as a channel for the rowers to stay out of the competition lanes.

To keep birds off the top.

I'll go with Thomas.