A few reasons to be vigilant with line of sight. Some obstacles are invisible on ship's electronics. Coursing through Captains Passage between Athol Island to the north and Prevost Island to the south with a tide change in progress, I noticed considerable debris in the water. Quickly snapped a couple of pics and noticed the extent of debris merited equally quick attention to the helm.  The surface debris is one thing, but submerged debris can be a bigger issue. When approaching tide lines keep a watchful eye.