Complete the Gyala Hatchery mission. Alternatively, if you have completed the Unwaking Waters mission for the Kurzicks and have access to the Harvest Temple, you can go the long way via the Unwaking Waters explorable, through the Luxon outpost of Unwaking Waters and then through Silent Surf. This can only be achieved if you are allied to the Luxons (if your Luxon faction is higher than your Kurzick faction) when entering the Luxon outpost of Unwaking Waters.