Bring a large saucepan of salted water to a boil and toss in the lemon quarters to infuse the water.
Carefully add the shrimp and poach them for 1 to 2 minutes, just until they turn opaque and pink. Immediately transfer the cooked shrimp into a bowl of ice water to halt the cooking process.
Once the shrimp are cooled, drain thoroughly and blot dry with a clean towel.
In a mixing bowl, combine the cooled shrimp, imitation crab, finely chopped celery, minced red onion, Old Bay seasoning, lemon juice, salt, pepper, mayonnaise, and freshly chopped dill.
Stir the mixture gently until the seafood and vegetables are evenly coated with the creamy dressing.
Finish by sprinkling extra dill over the top for a burst of freshness. Serve immediately or store covered in the refrigerator for up to two days.