How to make slow area in custom map?

In part of my custom map, the hero has to slog thru waist-high water, and I’d like his movement speed slowed by about 35% for a particular area of the map. I was wondering if i could use a Damage Layer with a damage of 0, but using a slow “damage.” There is an option to choose the damage effect, and i found “records/fx/damagedefault/dmgdur_slowspeed_fx01.dbr”.
I was wondering if anyone has been able to use these damage layers for non-damage effects?

As I know Damage layer able to use one of flat damage type, not duration type. And even in you will use Damage layer with 0 damage or unreachable objects emits debuff auras, it still will deal damage every second (Yes, reductions counts as some kind of damage.) and trigger any on hit procs. I think more suitable to use area mutators similar to dangerous areas.
UPD: one more option - negative buff like totems around ugdenbog coven.

Thanks for the info. Neither of your options seem suitable to my purposes.
I may hafta nix the whole idea. :confused: