Mishnah Mikvaos 5:2: If it [the spring] was led to pass over vessels or over a bench, Rabbi Yehuda says: it is thereby [still] as it was [i.e. the status of the spring is unchanged]. Rabbi Yose says: it is thereby like a mikveh, so long as one does not immerse over the bench.

הֶעֱבִירוֹ עַל גַּבֵּי כֵלִים אוֹ עַל גַּבֵּי סַפְסָל, רַבִּי יְהוּדָה אוֹמֵר, הֲרֵי הוּא כְמוֹ שֶׁהָיָה. רַבִּי יוֹסֵי אוֹמֵר, הֲרֵי הוּא כְמִקְוֶה, וּבִלְבַד שֶׁלֹּא יַטְבִּיל עַל גַּבֵּי הַסַּפְסָל:

Mishnah Mikvaos 5:3: A spring that flows like a centipede [i.e. with many smaller tributaries], if one added [drawn waters] upon it and it continued flowing, it is thereby [still] as it was. If it [the spring's water] was standing, and one added [drawn waters] upon it and it continued flowing, it is equivalent to a mikveh in that it purifies [only] while gathered in one place, and to a spring in that one can immerse [objects] in it in any amount [of water].

מַעְיָן שֶׁהוּא מָשׁוּךְ כְּנָדָל, רִבָּה עָלָיו וְהִמְשִׁיכוֹ, הֲרֵי הוּא כְמוֹ שֶׁהָיָה. הָיָה עוֹמֵד וְרִבָּה עָלָיו וְהִמְשִׁיכוֹ, שָׁוֶה לְמִקְוֶה לְטַהֵר בְּאַשְׁבֹּרֶן, וּלְמַעְיָן לְהַטְבִּיל בּוֹ בְּכָל שֶׁהוּא: