Employer asking me to do something i cant....

I'm a support worker for individuals with learning disabilities, we do a vary of different activities which are enjoyable and i enjoy my work. My employer has decided to push swimming as an activity for our service users, the only problem i have with this is that i can't swim. I don't feel comfortable in a swimming pool and i don't want to risk my health as i do have a fear of drowning, we deal with challenging behaviour and the last thing i want is to be in the deep end when one of the service users blows! But my employer insists i do it and by refusing i am breaching my contract, they don't believe me and are pushing me into doing something i can't. I've had to write a statement for our HR saying i can't do this activity as i cant swim and now they've asked me to provide a doctors note to say i can't swim, a doctors note?!



I really need to know where i stand here, the company are being awful and uncompromising and i genuinely feel like i'm being bullied, how on earth can a doctor prove i can't swim? It's almost hard to believe what i am writing but it's all true. Can anyone please advise me what i can do and what my rights are?

Employer asking me to do something i cant....