Sqweels, the city I grew up in had a small airport, and those balls along the power lines out near the airport. The airport was not particularly near the river, and in fact I didn’t see any of those near the river. There’s one example for your anecdote collection.
I once convinced hubbie that they were to keep the power lines afloat in case of bad floods.
Re: sqweels’ observations about seeing them mainly over rivers.
Note that power lines are easier to spot from above over land than water. But not for the reason one might think. The land under power lines is usually maintained differently than surrounding land. In the Pacific Northwest forested areas they are clearly visible as clear cut linear swaths.
Hard to clear cut a river.
FtG
Note for Sim City 3000 players: if you run power lines over a body of water, you’ll see these balls on them.