Which town lies on the west side of the entrance to the Niagara River?

The correct choice identifies Niagara-on-the-Lake as the town located on the west side of the entrance to the Niagara River. This historic town is situated at the confluence of the Niagara River and Lake Ontario, specifically on the southern bank of the river's mouth. It is well-known for its scenic beauty, wineries, and Shakespeare Festival, making it a popular destination for tourists.

The other locations mentioned do not sit on the west side of the Niagara River entrance. For example, Tonawanda is positioned further to the south and east of the river entrance and is not at the mouth of the Niagara River. Olcott is farther west and is also on Lake Ontario, but not near the river entrance. Port Weller, on the other hand, is located on the east side of the mouth of the Niagara River. Therefore, Niagara-on-the-Lake is the correct identification based on its geographical position relative to the river.