Time Out says
Take a walk off the beaten path, away from the big beaches at Manly, and you may find yourself in a tucked-away cove that has a beach and its own waterfall. This is Collins Flat Beach – the closest waterfall to Sydney harbour and a nice little getaway from the city. It’s more of a dribble than a gushing waterfall on our visit, but the best time to go is after heavy rainfall in autumn. There are no picnic facilities, however, it’s a perfectly secluded spot for lunch at the beach or for a romantic walk away from the crowds. It’s not large enough to create a swimming pool, but the waterfall is easy to reach so you can get your feet wet if you want to. You can’t bring dogs though, as this hideaway is a habitat for fairy penguins. So leave your little buddy at home for the afternoon.