Rowing and its associated training can be a strenuous activity. You should therefore be in good health and have no medical or physical condition precluding heavy exercise.
If there is any doubt you should first consult your Doctor.
Some conditions such as asthma and diabetes, for example, do not prevent individuals participating in the sport, but you do have a duty to declare any condition that might put yourself or others at risk. Likewise you have a duty to declare any changes in personal health whilst a member of the club that may put yourself or others at risk.
It is important therefore that you inform those around you eg coaches and crew members, of any condition they may have to deal with in the event of an emergency.