In a medium mixing bowl, combine the sour cream and mayonnaise.
Add the lime juice to the bowl for acidity.
Incorporate the chipotle sauce for a smoky flavor.
Add garlic powder and cumin for seasoning.
Mix all the ingredients until well combined.
Taste the sauce and season with salt and pepper as needed.
If desired, fold in chopped cilantro for freshness.
Let the sauce sit for at least 10 minutes to allow flavors to meld.
Serve the sauce chilled over fish tacos.
Store any leftovers in an airtight container in the refrigerator.