1. Draw the outline (Free Select Tool with antialisaing and Feather edges radius to 20) and save it as path
2. Select > Border > 4px (Border style Hard)
3. Select > Feather > 5px
4. Fill with outline color
5. Select from previous path
6. Select > Shrink > 2px
7. Fill with background color

Filters > Blur > Median Blur > Radius: 6

• "Water Swirl" by InspectorJ of Freesound.org
• "Underwater ambience" by akemov of Freesound.org
• "Perspectives" by Kevin MacLeod of incompetech.com
• Main theme and all sounds FX were kindly made by Nullrate