You will want to give your rescue dog a bath. This may go really smoothly--some rescue dogs love the attention and like water--or it might not. There can be some serious challenges when bathing a rescue dog; they may be really dirty, have matted fur, or have parasites. Also, rescue dogs may have previously been abused or never been bathed before, leading them to react in a frightened, aggressive, or excited way. Because you will probably not know your dog's history and experience with bathing, proceeding in a slow, careful manner and using a little trial and error to find out what works best when bathing your rescue dog will be necessary.
A rescue dog has probably been through a lot. At the very least, the dog is experiencing a rehoming situation and a change in his residence, which will be very stressful even for a well-adjusted dog. Other rescue dogs may have experienced abuse and neglect, be suffering from malnutrition, parasites, health problems and even injury. A rescue dog may have limited or no experience with being groomed or bathed.
It's not uncommon for a stressed or abused dog to react in a frightened or aggressive manner when handled, including receiving a bath. The enclosed area may make the dog nervous, or the sounds and feel of running water can startle him. Work slowly, talk calmly to the dog, and watch the dog for signs the dog is becoming overwhelmed or about to react aggressively. You may want to have an assistant help you handle the dog, reassure him, and watch for signs of trouble. Adjust your bathing as necessary, and try to be organized and keep the bath short so as not to cause undue anxiety in a rescue dog.