We’ve hit a sandbar!
As time goes by, the canals inevitably tend to fill up because of the constant deposition of anthropic sediments in the lagoon, of material washed away from the canal embankments and the material brought in by the natural ebb and flow of the water. It therefore becomes necessary to cyclically remove the sludge from the bed of the canal to avoid endangering navigation and prevent the degeneration of hygienic conditions.