Answer
$4^{\circ}C$.
Work Step by Step
On page 296 it is explained that because of water's high specific heat capacity and poor heat conductance, the bottom of a deep body of water in a cold region remains at $4^{\circ}C$.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.