Liverpool's river (6)

I believe the answer is:
mersey
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">liverpool's river</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for mersey that I've seen before include "River with ferry and tunnel" , "River flowing into Liverpool Bay" , "Route between Liverpool and the Wirral" , "Liverpool's river" , "River rising in Derbyshire and flowing into the Irish Sea" .)