Lago (Lake) Grey in Parque Nacional Torres del Paine is fed by Glacier Grey (far end of lake), which in turn is fed by the Southern Patagonian Ice Field (far horizon).
Glacier Grey is but one of dozens of glaciers fed by this 350-km-long icefield (Perito Merino Glacier in Argentina is perhaps the most famous).
I assume that the icebergs have broken off the glacier and floated down the lake until striking shallow water near the outlet.