turtle live on the riverbank.

The first letter of a sentence should be capitalized.
Also, {turtle} is the third person singular, so please add an -s at the end of the verb.

I’m going to assume Turtle is the name.

Turtle lives on the riverbank.

In this situation, you need to give the name Turtle to the turtle, or reference it using ‘the turtle’.

turtle’s eyesight are bad.

{Eyesight} is an uncountable noun.

Turtle’s eyesight is bad.

turtle also appear at harbor.

{Turtle} is the third person singular, so please add an -s at the end of the verb.
Also, please use the article before {harbor}.

Turtle also appears at the harbor.

there was a grimy turtle at the fild.

You mean {field}?

In this sentence, ‘a turtle’ is correct.
There was a grimy turtle at the field.