The Abarbanel on Shemos chapter 7 discusses the idea that the frogs were actually crocodiles. I did not find the exact location of what Ohr Somayach writes. However, the above is where Abarbanel discusses the idea that it were crocodiles instead of frogs.
The Kli Yakar on Shemos 7:17 cites the Abarbanel and explains that the reason why the first three plagues happened the way they happened, was to counteract the way pharaoh was thinking about Hashem. Pharaoh doubted Hashem. Since the Egyptians were worshipping the Nile, G-d involved the Nile in one of the plagues, just to show that "their gods" (e.g. the idols the Egyptians worshipped), cannot control the Nile, G-d can!
The idea of "worshipping the Nile" can also be found in the commentary of the Or HaChaim:
בזאת תדע כי אני ה׳, "In this you shall know that I am י־ה־ו־ה." The reason G'd used the plague of blood to prove to Pharaoh that He was who He said He was, is understandable when we consider Shemot Rabbah 9,9 according to which the Egyptians looked upon the Nile as a benevolent deity. By striking this deity first and turning it into a source of curse instead of a source of life, G'd demonstrated that He owned the Nile. According to the Zohar volume 3 page 297 the tetragram implies the eternity of G'd. He had preceded the river Nile just as He had preceded every other phenomenon in the world.
This idea is cited by the Or HaChaim from Shemos Rabbah 9:9, but that does not show up this idea on Sefaria.
Torah Tidbits; ISSUE 1449 JAN 1ST '22; Rabbi Shalom Rosner; p. 26-27