Sign from National Taiwan University:
qǐng wù fàngshēng
"Please do not release living [creatures into this pool]."
Fàngshēng 放生 ("life release") refers to the freeing of captive animals. Adherents of Buddhism often do this in special pools or ponds designated for the purpose on the grounds of temples and monasteries. One can purchase captive fish, turtles, birds, and so forth and set them free when they visit Buddhist establishments, thus gaining merit and good karma.
Reminds me a bit of the "pardoning" of the National Turkey just before Thanksgiving in the White House every year.
[h/t Gene Hill]