Can one use a lake or a river to toivel their vessels?
Answer:
Natural lakes and rivers can be used for tevilas keilim, provided they contain 40 se’ah (of course, they usually do). However, a stream whose source is rainwater or melted snow cannot be used unless the water is gathered into one place (not flowing).
Sources: Tur and Shulchan Aruch, Yoreh Deah 201:2.
