After Derek Muller of Veritasium took a boat tour of Los Angeles reservoir that was filled with 96 million black balls made from HDPE recyclable, food-grade plastic, he decided to buy 10,000 of these very same balls to put into his own backyard pool to see if he could swim through them.
As it turns out, Muller and his friends were able to swim through a single layer of shade balls fairly easily. Yet once a second layer was added and some modifications were made, Muller discovered that these balls acted much in the same way as non-Newtonian fluid, keeping him afloat despite the liquid below him. The longer he remained in the pool however, the surface became more like quicksand dragging him under due to the fact that the shade balls are almost half-filled with water. Swimming in the double layer was simply not possible.
My sense was that swimming in shade balls would be difficult but still doable. This was roughly true for the single layer of shade balls. …It’s much more intense exercise and it’s also annoying to be bombarded with shade balls on all sides of your body, particularly your head. With multi-layer shade balls (as exists on much of LA reservoir) things get significantly more difficult. The balls bunch together and when you try to move through them quickly, they become more rigid, providing significant resistance to motion.