What is Nachal Mitzrayim?
Ha'Emek Davar (here and Bereishis 15:18): It is a river (not the Nile) that dries up at times. It does not exist today. Radvaz (Teshuvah 6:2206)
In Makas Dam, Moshe struck the Ye'or, the river they worshipped. It was after Pesach, for the punishment of Egypt lasted 12 months (Eduyos 2:10). If there was about a month between plagues (refer to Shemos 7:25:1:1), Makas Dam was in Tamuz. All the more so the Nile would be dry! Do the fish die every summer when it dries up?! Egypt does not get rain; they rely on the Ye'or. Do they store water for the entire summer for drinking, irrigation, their animals, bathing, laundry and cooking?! Why must we say that Yisrael crossed it? Perhaps Moshe, and all of Yisrael, were on the east side when he struck it! Surely this is a printing mistake; he still discusses Wadi El Aris. (PF)
And women and children, and every man had at least 90 donkeys of gold, silver and clothing (Bechoros, 5b)!