Super Mario Sunshine/Noki Bay blue coins

Under the falls
Look underwater to the left of where the water fall lands. Follow the trail of gold coins to find a blue coin at the end. There is a bubba swimming around down here who should be avoided. Also, don't collect all the gold coins on the swim down as you may need them for air on the swim back up. There is a 1-up below the coins but it's very difficult to get it and get back to the surface without drowning. Available all episodes except 3.

On the water (x2)
Two coins float just above the water. The first is to the left as you start. For the second, go to the left end of the cliff where it bows out in a semicircle. Then go straight out to sea from there to see the coin. Both coins are much easier to get once the water has been cleaned up starting episode 5, until then use the boat to reach them. In episode 1 the boat is right next to the first coin instead of at the boathouse where it normally is. Available all episodes except 3.

Lower pulley crevice
Go up the right cliff face as in the episode 1 walk-through. When you reach the second basket, drop and and from the cliff and sidle along the crevice to the left. At the end of the crevice, spray the wall and part of it will retreat into the cliff leaving an opening you can hop into. Wall jump to the top of the opening to collect the coin there.

under the little land sticking out that is right next to the waterfall, is a blue coin. The grandfather is on that little piece of land. First appears in episode 1, uncork the waterfall. Also, if you spray every brown block, the wall will open up to reveal a pathway, and blue coins. Be sure that when your done fighting Glooper Blooper in the fifth episode, and you drop down, you spray all of the vases. One of the vases will have a blue coin

All 30
1) Above the water behind the start of the level (episodes 1,2,4,5,6,7,8). On the water

2) Above the water near Blue Coin 1 (episodes 1,2,4,5,6,7,8). On the water

3) Follow the trail of coins leading down under the waterfall... beware of drowning (episodes 1,2,4,5,6,7,8). Under the falls

4) Same as bullet point five in 100 coins Shine (episodes 1,2,4,5,6,7,8).

5) Above where you got the Rocket Nozzle (episodes 1,2,4,5,6,7,8).

6) In the hidden ruin by the second waterwheel. You have to spray it to reveal it (episodes 1,2,4,5,6,7,8).

7) Another hidden ruin right under the first one (episodes 1,2,4,5,6,7,8). Lower pulley crevice

8) Under the waterfall, hover over to the top hole (episodes 1,2,4,5,6,7,8).

9) Under the waterfall, jump down, hover over to the cave that is below the hole in number 8, and wall kick up (episodes 1,2,4,5,6,7,8).

10) Spray the brown square to open the ruins. It is in the middle (episodes 1,2,4,5,6,7,8).

11) Spray the M Graffiti that is next to the ruins (episodes 1,2,4,5,6,7,8).

12) In one of the cubby holes in the second ruins (episodes 2,4,5,6,7,8).

13) Go on top of the shell, look towards the ruins, locate the hole, and hover to it (episodes 1,2,4,5,6,7,8).

14) From 13, drop down and Rocket up to the Blue Coin next to 13.

15) From 14, hover over to the hole on the left (episodes 1,2,4,5,6,7,8).

16) From 15, hover over to the left to the smaller area and spray the right brown square (episodes 1,2,4,5,6,7,8).

17) From 16, hover over to the wall next to you and spray the top (episodes 1,2,4,5,6,7,8).

18) Spray the brown square on the big wall, enter the first hole from the left, go through the tunnel, and spray the top brown square (episodes 1,2,4,5,6,7,8).

19) Wall kick all the way up, climb the cliffs, and two brown squared have blue coins (episodes 1,2,4,5,6,7,8).

20) Same as 19 (episodes 1,2,4,5,6,7,8).

21) Go the same way you went to get the gold bird, jump down from the mountain, make it to the first platform you see, and spray the wall on bottom left (episodes 1,2,4,5,6,7,8).

22) From 16, there is another wall if you look top left. Rocket your way up there or go on a cliff and Rocket from there spray the top left.

23) Jump down to the treasure room. Spray the pottery (episodes 1,2,4,5,6,7,8).

24) Same as above (episodes 1,2,4,5,6,7,8).

25) Get the Turbo Nozzle (unlock in episode 1 or 2, where you get coin number 8) and spray the corresponding O (episode 6).

26) Same as above (episode 6).

27) Go under the waterfall to go into deep sea. They're on top of pillars (episode 4 and 8).

28) Same as above (episode 4 and 8).

29) Same as above (episode 4 and 8).

30) Same as above (episode 4 and 8).