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According to the tosafist R' Yosef Bechor Shor, as cited in answers here and here, the Nile turned to blood only long enough to kill all the fish and then it turned back to water (which was now fouled by dead fish). I had been under the impression that the river stayed as blood for a week, which led me to ask where the magicians got water for their trick, and from answers there, R' Shor's view isn't universal.

If the Nile turned to blood only briefly and then turned back as R' Shor says, then what happened in the following week, where the text tells us (Shemot 7:25):

וַיִּמָּלֵא, שִׁבְעַת יָמִים, אַחֲרֵי הַכּוֹת-יְהוָה, אֶת-הַיְאֹר.

And seven days were fulfilled, after that the LORD had smitten the river.

It doesn't seem to be saying merely that seven days passed uneventfully; the text says וַיִּמָּלֵא, which JPS translates as "were fulfilled", rather than something more passive like וַיְהִי. It sounds to me like something happened at the end of the seven days.

What was it that happened? According to the R' Shor view, did it take seven days for the dead fish to clear so the water was usable again? Or does the text just mean that seven days passed before preparations for the next plague began, and in fact it is more passive (just that time passed)? Or does the text mean that the river stayed as blood, contrary to R' Shor?

R' Shor doesn't comment on that verse and the person who provided one of those answers didn't know how he handles this.

Ramban connects the seven days mentioned concerning this maka to the need to dig for fresh water in the passuk beforehand.

ופסוק וימלא שבעת ימים קשור בעליון, וימלא בזה שבעת ימים, שחפרו מצרים סביבות היאור ולא יכלו לשתות ממימי היאור עד מלאת שבעת ימים אחרי ההכאה:

Rabbi Shor, while not making this direct statement, did also mention that the digging was done in order to find fresh water that didn't have rotting fish in it

ויחפרו. לעשות מעיינות להם שלא יהיו שם דגים ולא יבאשו אותם מנבלת דגים:

This is important as they seem to side with Ibn Ezra at least in the point that fresh water was available to Egyptians who dug for it. In contrast to the medrashic approach assuming no Egyptian had access to fresh water unless bought from the Jews.