Although there are not many waterfalls on Oahu, the few that exist are definitely worth a visit. Lovers of nature or just those who enjoy a walk will delight in the hikes to the waterfalls: a cool destination after a long, hot journey. Swimming in the rock pools is not encouraged, but many visitors take a quick dip before the trek home. If you are responsible around the water, there shouldn't be any problems.
Near Honolulu, in the Manoa Valley are the Manoa Falls. A vertical cliff of 150 feet greets you as the water tumbles into the small pool below. Although it may seem to be a refreshing option, it is not recommended that you swim in the pool, or drink from it for that matter. The plunge pool is filled with boulders and the bottom can not be seen, making it dangerous for swimming or diving. Parking at the falls is no problem, but remember not to leave valuables in the car - even paradise has crime! The hike to the falls will take about half an hour. It is classified as 'easy' and travels through a bamboo forest and a rainforest. Just remember you mosquito repellent, because those blighters never sleep!
A rather popular waterfall on the northern outskirts of Punalu'u on the Windward side of the island is Sacred Falls. Although this area is a state park, it has been closed to the public since May 1999 and will probably be indefinitely. This is the result of a tragedy, when a landslide killed a group of hikers who were standing beneath the falls. This is not the only incident that has marred this park. Another notorious incident involved a group of tourists who were held up at gunpoint while visiting.
Although the park is closed and you cannot hike to the falls, you can still get a glimpse of them over the roof of the Church of Latter Day Saints along the highway. The area's Hawaiian name is Kaliuwa'a and the entire area was considered sacred. This was the narrow valley where the gods would show disfavor by dropping rocks onto your head! The walls of the valley are 1600 feet high but the falls drop a mere 90 feet.
On the North Shore you will find Waimea Falls Park, known as the most culturally significant park on the North Shore. In ancient times the Hawaiians believed the water had healing powers, and would bring their wounded to bathe in the cool pool. The water has a reddish tint due to the iron oxide found in the volcanic soil that flows down from the surrounding mountains. Today the falls are the centre of one of Waimea's most thrilling sights; the professional diving from the 55 foot rock wall into the pool below.