I have been wondering about the plague in Exodus where the water was turned into blood. Could this be that the witnesses were red-green color blind like I am? Could the water have turned green and slimy, which by itself is a horrible thing, and the people have thought it was red and looked like blood?

Anything is possible. The main theory I've heard is that reddish brown silt from upstream turned the wate a reddish brown.

But the plagues were supposed to be miracles. Does it really matter what caused the river to turn color? If these were miracles performed by god, then wouldn't he have had to power to do whatever was necessary to change the color of the water?

There is another reference to red water during a battle,I think with the Philistines? The Lord caused the sun to come up red over the water and the enemy army was frightened, thinking a river of blood was flowing down from the battle up ahead of them, they fled in terror. But the water in Exodus must have been really like blood to punish the slave owners?

Read further. It wasn't just the river.

Galveston, your answer is unclear. What are you referrring to?

Exod 7:19
19 And the LORD spake unto Moses, Say unto Aaron, Take thy rod, and stretch out thine hand upon the waters of Egypt, upon their streams, upon their rivers, and upon their ponds, and upon all their pools of water, that they may become blood; and that there may be blood throughout all the land of Egypt, both in vessels of wood, and in vessels of stone.
(KJV)

Yes right you are. Understand that there is only one molecule's difference between chlorophyll, the life blood of plants, and hemoglobin which is our blood. Chl. Uses copper instead of the iron found in blood. And Revelation as well as the Old Testament tells of a river of blood in the end of days, the grapes of wrath being trod in God's great winepress when he destroys the wicked. I'm not saying He didn't provide a miracle in Exodus at all, but green water would be pretty horrible, He wouldn't need a miracle necessarily just a bad punishment. I mean, he could have called in lawyers and slapped a lawsuit on those bad guys... but I digress.