We will have that the potential energy that the lake possesses is:
[tex]P=(350000lt\cdot\frac{1\operatorname{kg}}{1lt})(400m)\Rightarrow P=140000000\operatorname{kg}\cdot m[/tex]So:
[tex]P=140000000\operatorname{kg}\cdot m\cdot\frac{1J}{0.1019716213\operatorname{kg}\cdot m}\Rightarrow P=1372931000J[/tex]So, the potential energy is 1372931000 Joules.
