You haven't said how your model looks like, but following concept should work:
Dim active = (From x In DBase.Stored_Activities
Join z In DBase.Stored_Crews On x.EMP_NO Equals z.EMP_NO
Select x).ToList()
Update
If you have a local in-memory collection and you need items with a field matching one within that collection, use Contains
instead:
From x in DBase.StoredActivities
Where localList.Contains(x.EMP_NO)
select x
Your list should contain the joining column* only, in this case should be made from crw_list.Select(Function(x) x.EMP_NO)
.