Un ejemplo con fotos:

Water in the spring is clear, but the ***spring head*** is difficult to see due to the overhanging bank and foliage that blocks a clear view.
http://www.tfn.net/Springs/CedarHeadItch.htm

El nacimiento es el sitio donde la fuente aparece sobre la superficie.

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Note added at 55 mins (2008-04-26 23:59:51 GMT)
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There is another term "head springs" which may be better because it refers to the source of both springs and rivers - the place where they rise out of the ground. Example:

The crystalline Ichetucknee River flows six miles through shaded hammocks and wetlands before it joins the Santa Fe River. In 1972, the ***head spring*** of the river was declared a National Natural Landmark by the U. S. Department of the Interior.
http://www.floridastateparks.org/ichetuckneesprings/