Quick answer: Unreal Engine 5 Lumen reflections flickering on translucent water? Lumen only writes opaque depth - switch the water to a screen-space reflection material or use opaque blend with refraction.

Lake reflections in a lighting test scene shimmer between two distinct images per frame. The DX12 capture shows Lumen's RSM missing the water surface.

Use opaque + refraction

Set the water material to Opaque, plug your distortion into the Refraction pin. Lumen writes opaque depth and reflects this correctly; translucent is fundamentally outside Lumen's coverage.

Or enable single-layer water

The Single Layer Water shading model has a dedicated reflection path that doesn't depend on Lumen. Use it for ponds, oceans, and any case where you want one continuous water plane.

Verify with the Lumen visualizer

ShowFlag.LumenVisualization 1. Surfaces that don't contribute show up empty - if your water is invisible here, it's invisible to reflections.

“Lumen is a closed system that loves opaques. Anything else is a special case.”

If you need real translucent water (waves with foam, edge fade), composite an opaque reflection with a translucent overlay rather than asking Lumen to do both.