Can an Echo Knight fighter's Manifest Echo be moved through water?

Question

I would like to know if an Echo, created by the Manifest Echo ability of an Echo Knight, can be moved through water?

An Echo itself is not considered a creature, and instead is listed as "image" and an "object" tweet 1 by Jeremy Crawford. Additionally, Jeremy Crawford has twice tweeted that Echos don't have a flying speed, even though they can be moved vertically through the air (contrary to another answer on this site) tweet 2 by Jeremy Crawford archived on a fan-site , tweet 3 by Jeremy Crawford. If an Echo doesn't have a speed, can it be moved through water?

Answer 1

Yes

Nothing prevents an Echo Knight's echo from being moved through water.

Two basic premises:

1. Things can move through water

There are no general rules about whether something can 'move through water'. Rulings about entities passing through other material are generally left to intuition. If a PC wants to telekinetically move a brick through a wall, the correct adjudication is that this is impossible - a solid brick cannot move through a solid wall. If a PC wants to move the brick through water, the common sense adjudication is that this is possible, because a brick can move through water. No additional case-by-case rules are needed.

2. The echo knight is not a creature and does not swim

Whilst the echo 'occupies its space' (a mechanical quality normally reserved for creatures), it is not a creature. It has no speed and expends no speed, but moves '30 feet in any direction' under the control of the Echo Knight. The rules governing a creature's self-powered movement through water (swimming) do not apply. We defer to the general, common sense rules for the movement of non-creatures through other materials. Since there are no special rules or constraints for moving the echo through water, the echo inherits the properties intuitively ascribed to non-creatures being moved under player control - it can be moved through water.

Answer 2

It is unclear, so the table needs to decide

Unfortunately, this mechanic of the Echo Knight is incredibly unclear as to how to adjudicate these things for moving it. I have reviewed other potential similar mechanic like spiritual weapon or telekinesis, but none of those have the same properties of the Echo Knight.

Which leaves us with a giant shrug as to what to do. In these cases, it comes down to the player talking to the DM about what they feel is fair, reasonable, and fun. There is no 'wrong' answer here, but you should think about the potential consequences for each decision.

Looking at how this might affect gameplay of movement, positioning, and battlefield control, it's important to think about the edge cases - but you're not going to cover them all. And that's okay! When they come up, discuss together and be reasonable. If the DM provides an unhappy result, table the argument until after the game and discuss why you didn't like it and what you think a good compromise could be.

Prepare in advance

Given the lack of clarity about this subclass in general, if a player is considering choosing it then they should discuss these issues with the DM prior to playing. Making sure everyone understands the gray areas, what ambiguities need to be agreed on, and that judgments may come up that require an immediate ruling will go a long way to to mitigating any unhappiness and setting the expectation that this subclass is a little loosey goosey.