TT #114 · Parshas Shemini · Aliyah 6 · Passuk 9
English: These you may eat among all that live in water: anything in the water, whether in the seas or in the streams, that has fins and scales—these you may eat.
Chullin 66b.
E-Daf.com — Chullin 66b (Tsurras Hadaf)
מִכֹּל אֲשֶׁר בַּמַּיִם. לְרַבּוֹת בּוֹרוֹת שִׁיחִין וּמְעָרוֹת שֶׁאָדָם שׁוֹחֶה וְשׁוֹתֶה מֵהֶן וְאֵינוֹ נִמְנָע.
Extension — “Among all that live in the water” extends the rule to water sources such as pits, ditches, and caves from which people ordinarily drink.
The phrase extends the rule to pits, cisterns, and caves.