Open the sea image and use the Rectangular Marquee Tool to select a sea part in the middle and place it on the top of the underwater part. Use the Free Transform Tool (Ctrl+T) to make this sea part thinner. Add a mask to this layer and use a medium-soft black brush to trim the edges of this part to make it softer and smoother.
Make a Color Balance adjustment layer (set as Clipping Mask) and to give the part near the horizon some yellow to fit the light there. On this layer mask, paint on the rest to keep its blue.
Create a new layer on top of the layers and use a small white brush to paint the lines for the sea's surface.
Open the umbrella image and use the Magic Wand Tool (W) to isolate the umbrella from the white background. Use the Lasso Tool (L) to select the shaft of the umbrella to add to the middle of the fish. Use Ctrl+T to make the shaft thinner.
Select the top of the umbrella to add to the top of the shaft in the main document.
Take the handle from the original image to add to the bottom of the umbrella in our working image.
Select all the umbrella part layers and hit Ctrl+G to make a group for them. Change the group's mode to Normal 100% and add a Hue/Saturation adjustment layer within this group to desaturate the umbrella.
Create a new layer within this group and hold down the Ctrl while clicking the thumbnail of the shaft and handle layers to load their selection. Use a soft brush with the color #0e6688 to paint on the handle and the shaft part below the sea's surface. Lower the opacity of this layer to 30%.
Make a Curves adjustment layer to darken the umbrella. On this layer mask, use a soft black brush to erase the end tip and then lower the brush's opacity to 5-10% to reduce the effect on the shaft.
Create another Curves adjustment layer to brighten the top of the umbrella and handle. Paint the rest to keep its lightness.
Add a mask to the umbrella group and use a hard black brush to erase the shaft parts on the sea surface and the left fish's fin.
Open the tree image and use the Lasso Tool to select the top of the tree to add to the top of the umbrella. Use Ctrl+T with the Warp mode to bend this leaves part to make it look like the fabric part of an umbrella.
Add a mask to the top of the umbrella and use a hard black brush to remove the fabric part.
Make a Hue/Saturation adjustment layer to change the color of the leaves.
Create a Color Balance adjustment layer and alter the Midtones and Highlights settings:
Add a Curves adjustment layer to bring more light to the bottom of the leaves. On this layer mask, paint on the rest to keep its lightness.
Make a new layer below the umbrella's group and use a soft brush with the color #121a19, the opacity about 20% to paint shadow for the shaft on the fish.
Create a new layer and change the brushes to the bubble ones. Set the foreground to #d7e7e7 and select the brush you like and press F5 to change the settings of this brush: