Or HaChaim on Exodus 14:30/אור החיים על שמות י״ד:ל׳

1 ביום ההוא, on that day, etc. The Torah simply means that the salvation only occurred on that day, not previously; even though the Exodus had occurred, the Israelites had not yet acquired much confidence in themselves vis-a-vis the Egyptians.

2וירא ישראל את מצרים מת, Israel observed Egypt dead, etc. Why did the Torah have to tell us that the Egyptians were dead? How could they be alive after they had drowned? The Mechilta explains this verse by saying that the Israelites observed the death of the Egyptians. Accordingly, the Egyptians did not finally die until they were washed up on the beaches. G'd arranged this in such a way that either party should clearly observe what was happening to their adversaries. The Egyptians' last emotion before they died should be one of shame vis-a-vis the Israelites. We have to read the words מת על שפת הים as belonging together.