Why would Joseph Smith take the risk in mentioning a river that continually flows into the Red Sea?

In 1 Nephi 2:9 Lehi mentions a river that continually flows into the Red Sea:

And when my father saw that the waters of the river emptied into the fountain of the Red Sea, he spake unto Laman, saying: O that thou mightest be like unto this river, continually running into the fountain of all righteousness!

It has long been thought that there are no rivers which continually flow into the Red Sea so why would Joseph Smith take a chance on mentioning something which could be empirically disproved like this? Unless Joseph Smith had good information on the area in question it seems rather risky.

However in 1999 George Potter proposed a stream east of the Gulf of Aqaba which meets the criteria. He remarks:

I have now visited the valley in the months of April, May, November, December and, most recently, January. Colleagues have visited in July and August. We have observed that the volume of water in the river seems rather constant throughout the year (even though from 1995 to 1999 the volume seems to have decreased perhaps 50 percent due to the continued effects of pumping the water in the upper valley). We have also observed throughout the year that vegetation flourishes in the canyon where the river runs, and moss and algae line the banks of the stream.
…I have escorted over a dozen people into the valley. Several others have made their own way there based on my directions. Are we witnesses of the river Laman and the valley of Lemuel? In my view, the characteristics of the site are compelling evidence that this is so.
– George D. Potter – A New Candidate in Arabia for the “Valley of Lemuel”

What are the odds that Joseph Smith would have been correct about a river continually running into the Red Sea? How would he have known that in 19th century America?

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