TT #164 · Parshas Shemini · Aliyah 6 · Passuk 29
Chabad.org — Vayikra Chapter 11 with Rashi
English: These are the creatures that are impure among the swarming things that swarm on the earth: the weasel, the mouse, and the various kinds of lizard.
Chullin 126b.
E-Daf.com — Chullin 126b (Tsurras Hadaf)
בַּשֶּׁרֶץ הַשֹּׁרֵץ עַל הָאָרֶץ. תָּנוּ רַבָּנַן, מִתּוֹךְ שֶׁנֶּאֱמַר עַכְבָּר שׁוֹמֵעַ אֲנִי אֲפִלּוּ עַכְבָּר שֶׁבַּיָּם, תַּלְמוּד לוֹמַר עַל הָאָרֶץ, אִי עַל הָאָרֶץ יָכוֹל עַל הָאָרֶץ יִטַּמֵּא, יָרַד לַיָּם לֹא יִטַּמֵּא, תַּלְמוּד לוֹמַר הַשֹּׁרֵץ, כָּל מָקוֹם שֶׁשּׁוֹרֵץ.
Textual limitation — “On the earth” limits the mouse named here to the terrestrial species rather than a creature living in the sea.
The wording does not make a creature cease to be in the category merely because it enters water; the creature's kind and movement remain relevant.