Standing on top of the sand dunes at Colchester and looking towards the ocean you will spot what looks like oases. (One oasis, many oases. Something I didn't know). But this isn't a desert so its not oases. Although its kinda is. Fresh water falls on the sand dunes in the form of rain (duh!). The fresh water then sinks away and appears again in low lying areas between the sand dunes. In these low lying areas you will find these pools of fresh water surrounded by vegetation. In some places the fresh water springs are clearly visible bubbling out from under the sand.