see nobody is swimming ask about the reasons and don't get in until you find them (there are several park guards and guides all over the place). there are sea fleas every now and then... or there can be jelly fish... and even bigger stuff... please be alert to this.
it is a rainforest... so, yes, it rains every now and then.
we would not recommend though an umbrella... better a poncho if you are planning to see the rainforest and enjoy its nature. there are some areas where the walk is made on a wide sort of dirt road, but there are some other trails that are very narrow. and then 