One of the reasons I like to use the quarry lakes for Luna to swim in is quite simply that it's dead easy to get her to actually swim which is good for her arthritis. And as I always drive there, I always have a tennis ball for the purpose and most importantly it is only used during the swim which is either at the start or end of the walk.
When I go to Ottobeuren, I also have the tennis ball in the car but know that Luna will pester me for the entire walk to a part where she can swim and then all the way back. The chasing with abrupt stops & turns is exactly what I don't want her to do for her hips-sake. And continuous biting/chewing on a tennis ball is like chewing sandpaper for a dog's teeth. A vet once warned us of this as his own dog had to suffer teeth being pulled due to the damage - he spotted it on our old Flash who always had a tennis ball in his mouth and could even manage four at one go without any human help!
Means I have to use sticks which are frankly even worse as they can easily break - Luna always chews them - & get stuck between the two sides of the jaws and cause death! I have witnessed Luna get one stuck, a pretty frightening event. So for the few minutes, I do watch out very carefully.
However, today I happened to spot a tennis ball stuck in a swirl of water in the river directly next to the "beach" in the Blip. So that was ideal and it made it a bit easier to aim for the very few spots in the river at this time of year that are deep enough to force her to swim. In the extra photo, you can see that my long throw was well placed. I was quite good in my youth at cricket & the only "athletics" event at junior school sports day that I was able to stand a chance - Longest Cricket Ball Throw.
After the swims at several spots, we turned homeward but I had to take the ball with me, mainly for environmental reasons as we have dozens given to us a few years ago from a tennis club throwing away their used balls. On the way, we met up with a Border Collie "Leha" and her heavily pregnant owner & partner. Have known her for at least the last two/three years she has had Leha (& no partner at first). Leha is typically Border Collie hyper-active & tennis ball throwing with a special thrower has become standard on every walk - quite understandable when pregnant. Turned out the tennis ball had been lost during the morning walk & despite the numerous "keep it, we have more", I was glad to hand it over and put a stop to the previous 20 minutes of continuously having to throw the ball along the past & into fields.