Question

ぽ

一番下の行の、Let’s go down の down って必要なんですか？どういう意味になるんですか？🙇‍♀️

IIIII III しIIE 1ake again.
“Why not ?”asked Edward.
“Because the lake is polluted,” said Mr. Black. “There's a new sign at the lake. It
says:No Swimming, Polluted."
“What is polluting the lake ?" asked Jill.
“Let's go down to the lake and look at it,” said Mr. Black.