I was a lifeguard in Vancouver, BC. Yes, you absolutely need WSI if you want to be hired. City pools like to utilize as many skills as possible from their staff. If you only have NLS, your abilities for anything else is too limiting. The more skill you have (ie aquafit, WSI, LSI, etc.) the better.
I know plenty of cities are desperate for aquafit instructors, you'll be hired in a snap with this additional certification.
In order to get the certification:
1. Take Fitness Theory Course (through BCRPA approved classes)
2. Complete the test (80% to pass)
3. Aquafitness module Course
4. Practicum Hours (8 recommended)
5. ICE (In-water test, evaluator comes to assess your class)
Lifeguards that work for the city (in the lower mainland) usually get paid approximately $18-22