Is there are sutta in which the Buddha says if bathing in Ganges River could purify beings; then the fish, turtles, crocodiles, etc, would be purified?
It's in Therigatha:
Punnika, surely you know.
You're asking one doing skillful kamma
& warding off evil.
Whoever, young or old, does evil kamma
is, through water ablution,
from evil kamma set free.
Who taught you this
— the ignorant to the ignorant —
'One, through water ablution,
is from evil kamma set free?'
In that case, they'd all go to heaven:
all the frogs, turtles,
& anything else that lives in the water.
& any other evil doers,
would, through water ablution,
be from evil kamma set free.
Another related sutta:
The Buddha said to Sangarava:
“Is it really true, brahmin, that you practice purification by water, believing in purification by water; that you live committed to the practice of immersing yourself in water at dawn and dusk?”
“Yes, Master Gotama.”
“But brahmin, for what reason do you practice purification by water?”
“It’s because, Master Gotama, whatever bad deeds I’ve done during the day I wash off by bathing at dusk; and whatever bad deeds I’ve done during the night, I wash off by bathing at dawn. That’s the reason why I practice purification by water.”
“The teaching is a lake with shores of ethics, brahmin,
unclouded, praised by the fine to the good.
There the knowledge-masters go to bathe,
and cross to the far shore without getting wet.”
When he had spoken, Saṅgārava said to the Buddha:
“Excellent, Master Gotama! Excellent! … From this day forth, may Master Gotama remember me as a lay follower who has gone for refuge for life.”