All of ours are floating docks, the oldr ones have foam floaters The newer ones use plastic box toons. they are hinged at land to let the dock rise and fall with the water level and ussually tied either side from furthest point out to 50' on both sides on land with cables.

What has actually happened to many of those, the toons or floaters were not able to support the added weight of the ice and snow. A middle section may have been damaged or missing and gone unoticed. Most marines and dock owners dont hire divers to do annual inspections. As long as it's floating then your ussually fine.... however with the aded weight of ice and snow it pushed the middle section underwater, causing a valley in the roof, puttig a horizontal strain on the supports, which in turn also created a valley allowing more of the rain to puddle and freeze over these now semi horizontla suports. So even though it was only 2" of ice and 6" of snow on a level surface.... these collapsed from a few tons pushing on the one spot.

Like I said it was enough weight when evenly distributed that my 4' x 6' box for my bed held enough to squat the 1/2 ton suspension. I'd guess that my short bed held enough to weigh probably 600-800 lbs. of frozen liguid.

Multiply that by a few hundred times...... for a normal dock with 2 rows of slips, x 30 slips long....... Roughly 80' wide X 250' long then try to float it while covered in ice..........

They collapsed after they sank......