In a large bowl, combine the imitation crab meat (broken up), salad shrimp, diced red onion, and diced celery.
In a small bowl, whisk together the mayonnaise, lemon juice, Old Bay Seasoning, fresh dill, and salt. Taste and adjust seasoning, adding black pepper to taste.
Pour the dressing over the crab meat, shrimp, onion, and celery mixture.
Gently toss until all ingredients are evenly coated with the dressing.
Serve immediately or store the salad in an airtight container in the refrigerator for up to four days.