We are planning a week at Lake Atitlan in March. We are staying in a house between Santa Cruz and Jaibalito. We've got 4 kids, the youngest is 4, the oldest is 10. We definitely want to do some hiking and exploring. Is a guide necessary for hiking? Any we could do on our own? Our kids are pretty good hikers. Also, just hearing that perhaps there is a water quality issue? Is the lake swimmable???? Thanks!