Yes, your dog can swim in an in-ground pool, but there must be certain measures in place before this can happen.
Brush your dog
Thoroughly brush your dog's coat before allowing them into the pool. This removes excess hairs which can detach while swimming and overwhelm your pool's filtration system.
Use a pool sock
A nylon pool sock fitted over your pool's skimmer is a smart addition in most circumstances, but it's mandatory if your dog uses your pool because the ultrafine mesh will catch most dog hairs. After your dog has used the pool, manually run your filter to push debris into the filtration system. The pool sock will catch the hairs, and can then be disposed of and replaced.
Check the water quality
Your dog's presence in the water can alter your pool's pH and chlorine levels. Check these levels after your dog has finished in the pool and adjust as needed. Chlorinating your pool after your dog has swum is a good hygiene measure.
Remember that your dog does not bathe as regularly as the human users of the pool, nor does your dog wipe their backside. Be sure that the pool's water remains consistently safe for its human users.
Skim the pool surface
When your dog uses your pool, you must be even more diligent with basic hygiene measures, and this includes manually skimming the pool to remove hair before it reaches the pool's filter. If you don't already have an automatic pool cleaner, consider obtaining one. This reduces the amount of manual labour needed to keep the pool clean, which becomes even more important with the presence of your dog in the water.