Recently, a beautifully designed spar buoy (complete with multiple data sensors, computerized data storage, and radio transmission links) failed because it dragged its anchor.
As the marker buoy was also lost soon afterwards (again probably due to the strain on it from the current), a replacement spar buoy constructed of 20 cm diameter PVC pipe was attached to the ferry using wire cable in 1979.
The Estonian Police and Border Guard Board will mark the border zone area of the Estonian-Russian border on the Narva Reservoir with approximately 40 new spar buoys this summer.