Complex sentence: There are no surface streams entering the park, which is one of the reasons the lakes remain pristine and pure, and also for this same reason they are a bit "fragile" (low flush rates, low nutrient loads, etc.).
Split into simpler sentences: There are no surface streams entering the park, which is one of the reasons the lakes remain pristine and pure. For this same reason, the lakes are a bit "fragile" (low flush rates, low nutrient loads, etc.).