Yes, these are all underexposed. The noise works on #5 really well though.
I'd like to expand a bit on LarryD's advice...
First, never shoot higher than ISO 200 with the exception of only THREE instances :
#1 star shooting @ night
#2 early morning / mid evening animal shots
#3 You're inside, dimly lit and you have no flash
For all other applications, 200 ISO is the max you ever need to go.
Now, don't adjust your aperature for light gathering, especially in landscape / waterscape shots. Pick your focus and set your aperature to that. IE: if you want the 'whole thing' to be in focus, go at least F8. If you only want a piece of focus go lower than F5.6.
Use your shutter speed to gather light, not your aperature. While, yes, aperature affects the amount of light hitting the sensor,what it MORE affects, is your focusing.
Go back and try these again sometime with the above in your head. It will really change the way you go about taking lower lit images.
Hope these comments help you -- keep shooting.