Hi there...I was just hoping someone can help me.  My brother has a bit of a brain injury and can be easily influenced, and unfortunately some religious fundamentalists are trying to influence him.  Recently he was emailed this (below), and he forwarded it to me wondering what my response would be.  I can see that it's obviously a falacious argument, but I was wondering how to respond, seeing as my background isn't in science:

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Hi (name blanked),
Since the type of education you have practically makes you an engineer, I've always wondered, when the ocean flows into a river, which then flows into a lake; at what point does the salt water become fresh water, and how?
(name blanked out)

Hi :

    It is fresh water first and then, once it hits the ocean it is salt water. The great lakes have a level of salinity; which I have actually measured, as part of the building operations work I've done in the past. I think it is correct to say, that as the rivers have flowed to the oceans for thousands of years, the salt is left behind, thus, increasing the level of salinity. This is one of the concepts that disproves the evolution nonsense, because the salinity of the ocean would be off the scale, if the earth was billions of years old.

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