This cantrip caused a lot of debate in my campaign. Our verdicts:
By RAW, your target is "an area of water that you can see."
Blood plasma is 92% water, sure, but it's not water, it's blood. Likewise, mud is mud, and other fluids are other fluids. For the purposes of the game rules, ice is ice, not water, which is why the spell can't un-freeze things; it cannot target ice, or water vapor, only liquid water.
Thus, you can animate water, but not ice. Ice weapons, ice armor, and ice barricades still work, because someone is wearing or wielding them, but you can't move them anymore with the cantrip once they're frozen. That being said, a 5-foot cube of running water can work as a pretty effective barrier, too.
If only water you can see can be effected, then the Aqua Mage lock idea doesn't work, because as soon as the water goes into the lock, you can no longer see it, and it cannot be affected by the cantrip. Additionally, unless the target is already bleeding (which shouldn't be hard in D&D), you cannot see their blood, either. You can manipulate the blood you can see, but the effects would not extend to the blood you can't see, so no heart-freezing shenanigans allowed. Same goes for any other bodily fluid you can't see directly.