Blue Coin #1
Head down to the river at the beginning of the level, then follow it down to the very end, where you should see the Blue Coin in the water. Dive down to grab it.
Blue Coin #2
Look for the one building that’s next to the Rocket Nozzle in the town area of the map. It will have a little balcony with two windows/doorways. Jump and hover to those openings, then spray some water on the one side to make the Blue Coin appear.
Blue Coin #3
There are two buildings with windmills on top of them, one of which is moving and the other is not. Jump to the wooden platform of the windmill that isn’t moving and you should see a Blue Coin that is suspended in the air near it. You can spray the windmill to turn the wooden platforms, then grab the coin when you are close enough.
Blue Coin #4
Near Blue Coin #3, there is a building with some wires attached to one of the two towers on top of it. These little towers have openings in them and the taller one will be housing a Blue Coin.
Blue Coin #5
On the back of the same building as Blue Coin #4, there is some graffiti in the shape of the letter “M.” Clean up this graffiti to get this Blue Coin.
Blue Coin #6
Right next to Blue Coin #5, there is a female Pianta and two little kids, with a big pole right behind them. The Blue Coin is in the air right along the pole, but you won’t be able to reach it normally. There are a few ways to get this, such as talking to the female Pianta and having her chuck Mario into the air. Another way to get it is via the Rocket Nozzle, with there being one on top of the building where you found Blue Coin #2.
Blue Coin #7
Head up to the area where you found Petey Piranha during Episode 5, which is now clean of the pollution. There is a set of platforms up here, and the Blue Coin will be found on it.
Blue Coin #8
In the same area as Blue Coin #7, there are some clouds moving back and forth in the canyon leading to the platform where Petey Piranha was sleeping during Episode 5. You can spray these clouds to make them bigger, then use them to cross to that platform mentioned before. Spray the platform with water to make the Blue Coin appear.
Blue Coin #9 and #10
Return to the building where you saw the graffiti (Blue Coin #5), and right next to where it was is more graffiti in the shape of a circle. Cleaning it will make it appear in another spot in the town area, where you see another circle. This will be the building with the Rocket Nozzle on top of it. The Blue Coin will disappear after a set period of time, so you have to get to it quick. Once you grab it, do the same thing for the second circle to grab Blue Coin #10.
Blue Coin #11
Double back to the safe building with the two pieces of graffiti, then get on top of the tower with the ropes connected to it. Take the tightrope that brings you towards the entrance of this level, where you will see a blue bird on top of the platform there. Spray this blue bird with water until it drops the Blue Coin.
Blue Coin #12
If you don’t have the Rocket Nozzle, go get it now and head over to where you found Blue Coin #1. There is a ledge up high, along the wall, right next to the flower ring, which pretty much requires the Rocket Nozzle. The Blue Coin will be on that ledge.
Blue Coin #13
While on the town side of the wall, head towards the wall, close to the large water wheel. You will see another piece of graffiti on the wall, in the shape of the letter “M.” Clean this graffiti to get the Blue Coin.
Blue Coin #14 and #15
Get on top of the wall now and close to where Blue Coin #13 was located, there will be a little alcove. On the wall there will be an X-shaped piece of graffiti, which functions similarly to the circles in the town area. Thankfully, the other X is located on the other wall right behind you, on the non-town side, so both Blue Coins will be very easy to get.
Blue Coin #16
Get back on top of the wall and around where you saw the X-shaped graffiti marks. Near there, there is a piece of wall jutting out and on that piece will be another M-shaped piece of graffiti. Clean it to get the Blue Coin.
Blue Coin #17
If you are doing this in Episode 8, then in the little pit where the one X-shaped graffiti is located, there will be a Pianta that is covered in sludge. Spray him clean, then speak to the Pianta afterwards to have him award you the Blue Coin.