Why not C?

@Alexander-Blankers Happy to help! No need to switch out law school for med school, but you guessed it! You seem to be making too many assumptions about the implications of (C). Answer choice (C) states, "For many years, fish for human consumption have been taken from the waters of the North Sea." We do not know that this translates to "increased fishing efforts" as you suggest. Perhaps there are only a few fish taken each year. Perhaps the boats are built in some way to avoid creating pollution that would affect the fish. Perhaps the fact that fishing is popular here suggests that the fish are not polluted, since they are used for human consumption. Since we don't know if these assumptions are true or not, (C) does not impact the passage. When we're evaluating these types of questions, we need to be cautious about incorporating our own external knowledge into the information given. We should operate only with what is explicitly stated or directly implied. The fact that you're recognizing that you may be adding in your own assumptions shows that you're on the right track. Does this make sense? Please let us know if you have additional questions!

Honestly, I'm this scenario, I feel like I need to assume things unnaturally in order to get the approved answer. We know boats pollute. The prompt indicated this is a popular fishing spot. That could contribute (potentially significantly) to pollution which would weaken the immune systems. I really think this question was not the best. How old is it?

In this*. Excuse the weird grammar.

@Alexander-Blankers, Just to add to this - I agree with Skylar, you have to make many unwarranted assumptions to conclude that there is increased pollution. (C) says "for many years fish for human consumption has even taken out..", nowhere does it say that fishing has somehow increased recently. The amount of fish taken could be the same over the years, and for all we know, fish might have been consumed by indigenous tribes and caught from ashore or using non motorized craft. It is a stretch to conclude that large commercial vessels that contribute to sea pollution are prevalent in the area simply from the fact that fish has been taken from there for human consumption. (C) basically tells us that (a) there is fish in North sea and (b) it is suitable for human consumption - I think a more natural inference from these facts is that water is not polluted as it allows fish to thrive and as such, (C) actually weakens the argument.

This is from June 1993 LSAT

I see what you're saying. But even without an increase in fishing, it still says "for many years..." Many years suggests build up of pollution from fishing boats. That seems like one of the cause-effect relationships the LSAT likes to test for, right?

@Alexander-Blankers Your line of reasoning here still requires too many assumptions. (C) only states that fish for human consumption were taken from these waters for many years. It does not state that fishing boats were used in this process. Going back to the example that Irina gave, these fish could have been obtained by a local tribe who caught them from ashore or with the use non-motorized craft. Under this hypothetical, there would be no fishing boats that create pollution.