Read the water

Working into a narrow river or harbour entrance in a strong tide, you can generally discern by eye where the deep water is, especially if it’s breezy. Tide running against or across the wind cuts up the water where it is flowing fastest. This is also usually where it’s deepest, so if in doubt, stay in the rougher water. This beacon marks the shoals, but the situation would be obvious even without it at this state of tide.