Psalms 78:44

And had turned their rivers into blood
The river Nile and its seven streams; this was the first of the plagues of Egypt, ( Exodus 7:20 Exodus 7:21 ) , and was a just retaliation for drowning the infants of the Israelites in their river, ( Exodus 1:22 ) , a like plague will be inflicted on spiritual Egypt, and with equal justice; see ( Revelation 11:8 ) ( 16:3-7 ) ,

and their floods, that they could not drink;
the rivulets that flowed from the Nile, and every spring or confluence of water; or rather by these rivers and floods are meant the canals and ditches, which, as Jarchi ^F5 observes, were made by the hands of men, from the banks of the river Nile, to water their fields with.