Helsee

Ice-cold and greasy to the touch, the waters of the lake known as Helsee are as black as a hangman's heart. The fork in the river mid-Stir offers a direct route to the northern shore of Helsee, and hence the mouth of the Vale of Darkness itself, without needing to risk open battle against the unliving. Furthermore, the river fork is unquestionably the fastest route from Altdorf to the vale. The lake's waters are poisonous and contact with them is best avoided. Amongst the bones strewn around its shores are the remains of many betentacled terrors and the carcasses of beaked blubber-things that cannot accurately describe.

Source

 * : Sigmar's Blood
 * : pg. 7