The Little Minch

... effectively separates the Outer Hebrides from the Isle of Skye. Click here for a map (from Wikipedia).

The body of water that separates Lewis – the largest and northernmost of the Outer Hebrides – from the mainland is simply known as The Minch, or sometimes (according to Wikipedia) the North Minch. The Little Minch is the southerly extension of The Minch, and is also known (according to Wikipedia) as the Lower Minch.

South of the Little Minch is the Sea of the Hebrides. This could also be said to separate the Inner and Outer Hebrides (see map).

So ... either "the Lower Minch" or "the Sea of the Hebrides" should probably be allowed as alternative answers to this question.