The challenge with sailing in the Alps

From the 29er European website: "With the Lake so deep, the "anchors" are degradable concrete blocks with degradable line (hemp?) for the anchor line. The Race Committee has managed to set several of these around the lake and tie plastic jerry cans to them and then it's easier for the race management team to make mark changes faster. It's quite an accomplishment and ingenuity by the race management team. When appropriate, they can cut the line and these will degrade over time in the lake." Note:  my understanding is that it takes 20 minutes for the concrete blocks to sink to the bottom so they set these marks every 10 degrees to allow for wind shifts. Then they simply (or maybe not so simply) move the marks to these "jerry cans" (which I think are just little plastic bottles.)