Ocean visible through the island's lake in Unity3D?

Question

I'm working on a puzzle game featuring islands: there is a plane with a water shader, and objects colliding with that plane.

Now I'd like to make lakes on the islands, with different (higher) water levels than the ocean's.

The problem is that if I put a water plane in a "hole", I can see the ocean below at best, or even worse, the upper water surface just glitches out and disappear.

One option is that I move the lake's basin higher than the ocean's see level. This works, but I it doesn't look so good, because the lake becomes too shallow.

Another option is that I cut holes in the ocean's plane, but that seems a bit overengineered, isn't it?

Is there a better solution?

Also having a water plane for every "lake tile" causes some problems:

but I want to have dynamic lakes, so having a 2x2 water plane for a 2x2 group of lake tiles isn't a walkable path.

Answer 1

Based on this answer: Fade in rendering mode doesn't work as intended

I've put a quad just above the ocean's gameobject in my lakes, with a material with this shader:

Shader "Custom/DepthReserve"
{
    Properties
    {
    }
    SubShader
    {
        Tags { "RenderType" = "Opaque" "Queue"="AlphaTest+1" }
        LOD 100

        Blend Zero One

        Pass
        {

        }
    }
}

So this quad "reserves" the depth, not letting the ocean mesh to be shown.