This was provoking.

Now he realized that he had waited too long.

The tide had been flowing for almost an hour; it had flowed fast and, as he should have remembered, having been told, the principal channels were eight feet deep before the highest flats were covered.
He hurried along the edge, looking for a shallower place, but found none.

At last he reached the point of the flat he was on and saw, to his dismay, that here was the deepest spot yet, a hole, scoured out by a current like a mill race.

Turning, he saw, creeping rapidly and steadily together over the flat behind him, two lines of foam, one from each channel.