Instructables user Patenteux du Nord details the construction of these attractive lake bouys:

My parent’s cabin does not have drinkable tap water, so we use a lot of water bottles, juice bottles and all kind of bottles (my father prefers beer bottles). There is also no recycling system in this area, so we have to bring all these containers back home. I found a way to reuse them (using only my father’s tool box) by turning them into a useful, good looking and entertaining buoy for the lake. They can be used as seats for exhausted swimmers, anchor for your kayak or rock warning… It is also really fun to try to run on them like in a Japanese game show…