Ancient Lake Tonawanda does exist. It is well documented and its perimeter can be identified. At the Wilson-Tuscarora State Park is an image with a description of what ancient Lake Tanowanda looked like in its earliest stages, before the Jaredites arrived:
As the waters receded from off the land, the lake became smaller and smaller. Remnants of ancient Lake Tonawanda can still be seen today:
LAKE TONAWANDA WAS 25 MILES x 7 MILES IN 1851
Marshes: The great Tonawanda Swamp, which extends over portions of Genesee and Niagara counties, lies partly in this (Orleans) county. It is twenty five miles in length from east to west, and from two to seven in breadth. It is bounded on all sides by plains a little elevated above its surface. (J. H. Mather, and L. P. Brockett, M. D., A geographical history of the state of New York: embracing its history, government, physical features, climate, geology, mineralogy, botany, zoology, education, internal improvements, &c. With a separate map of each county. The whole forming a complete history of the state. Utica, John W. Fuller & Co., 1851, p. 400)
Those flat plains were an excellent, easy way to cross Book of Mormon lands, from east to west, as discussed on the Line Bountiful page.
LAKE TONAWANDA STILL EXISTS TODAY
This area is known as the Tonawanda State Wildlife Management Area, the Iroquois National Wildlife Refuge, and the Oak Orchard State Wildlife Management Area.

These are current ground level images of Lake Tonawanda, it still exists:
The overall shape of the lake is represented in the following Tonawanda Creek Watershed Area map. [Geography enthusiasts who use topographical maps as a base for their models need to respect the flow of the water and the lay of the land. We are using an official watershed map, without artistic embellishments.]
Please note the direction of the arrows. The entire area today funnels to a single outlet at the Niagara River in the City of Tonawanda:
The next map shows The Book of Mormon geography details. Please note the brown area is the Narrow Passage, which had a body of water on each side of it, and was just north of the City of Bountiful/Buffalo.
It should be noted that before the land changed at the coming of Jesus, Lake Tonawanda drained northward, not westward. (See Land Changed.) Today, Tonawanda Creek reminds us of what was once the deepest parts of Lake Tonawanda. When it rains and the water routes are full, it is easy to imagine how it used to be.
The only thing to do now is to identify what soil type is found within the brown area of the map. As it turns out, it is made of clay, and was formed from a terminal glacial moraine.