Final answer:
Turn on the Automated External Defibrillator (AED) and follow the verbal instructions to use it in conjunction with CPR to assist an unresponsive swimmer, which could save their life.
Step-by-step explanation:
When an unresponsive, nonbreathing swimmer has been removed from the water and CPR has been started, the next step would be to use the Automated External Defibrillator (AED) that has been brought to the scene. As CPR is being administered, turn on the AED and follow its verbal instructions. The AED will guide you through the process, including analyzing the victim's heart rhythm, and if necessary, prompting you to deliver a shock. It's important to ensure that no one is touching the victim when the AED is analyzing or delivering a shock to avoid interference. The early use of an AED, coupled with effective CPR, significantly increases the chance of survival in cases of cardiac arrest.