▁the ▁west ▁and ▁Car bon ifer ous ▁Lim estone ▁in ▁the ▁east . ▁▁▁ ▁A ▁hydro log ical ▁study ▁by ▁the ▁British ▁Ge ological ▁Survey , ▁published ▁in ▁ 2 0 1 6 , ▁noted ▁that ▁the ▁Ned ern ▁Brook ▁had ▁in ▁the ▁past ▁been ▁deep ened ▁and ▁canal ised , ▁though ▁the ▁pale och annels ▁of ▁the ▁old ▁river ▁me and ers ▁can ▁still ▁be ▁seen . ▁ ▁The ▁study ▁found ▁that ▁" as ▁water ▁levels ▁rise ▁in ▁the ▁Car bon ifer ous ▁lim estone ▁aqu ifer ▁below ▁the ▁site , ▁eventually ▁reaching ▁the ▁surface , ▁spr ings ▁and ▁se ep ages ▁result ▁in ▁the ▁formation ▁of ▁the ▁temporary ▁( e ph em eral ) ▁fresh water ▁lake . ▁The ▁process ▁by ▁which ▁the ▁temporary ▁lake ▁occurs ▁is ▁not ▁due ▁to ▁' fl uv ial ' ▁flo oding ▁caused ▁by ▁the ▁over - to pping ▁of ▁river ▁banks , ▁but ▁rather ▁is ▁a ▁result ▁of ▁rising ▁ground water ▁levels . ▁This ▁process ▁is ▁entirely ▁natural ▁and ▁is ▁domin ated ▁by ▁the ▁season al ▁changes ▁in ▁ground water ▁levels ▁couple d ▁with ▁the ▁top ograph ically ▁low ▁setting ▁of ▁the ▁Ned ern : ▁it ▁is ▁just ▁ 5 ▁m ▁or ▁so ▁above ▁sea ▁level . ▁The ▁lake ▁d ries ▁up ▁as ▁ground water ▁levels ▁in ▁the ▁underlying ▁aqu ifer ▁re ced e ▁during ▁the ▁spring ▁and ▁summer ." ▁▁ ▁The ▁study ▁proposed ▁that ▁the ▁name ▁Tir - L lyn ▁Ned ern ▁be ▁adopted ▁for ▁the ▁( other wise ▁un named ) ▁temporary ▁lake