This is a vertex and fragment shader.

wavy-ocean.shader

Shader "Custom/WavyOcean"
{
  Properties
  {
    _MainTex ("Texture", 2D) = "white" {}
  }
  SubShader
  {
    Tags { "RenderType" = "Opaque" }
    LOD 100
 
    Pass
    {
      CGPROGRAM
      #pragma vertex vert
      #pragma fragment frag
 
      #include "UnityCG.cginc"
 
      static const float mpi = 3.141592654;
 
      sampler2D _MainTex;
      float4 _MainTex_ST;
 
      struct vertOutput
      {
        float2 uv : TEXCOORD0;
        float4 vertex : SV_POSITION;
      };
 
      vertOutput vert (appdata_base input)
      {
        vertOutput output;
 
        output.vertex = UnityObjectToClipPos(input.vertex);
 
        float2 dtexcoord = input.texcoord;
        dtexcoord.x = dtexcoord.x + sin(dtexcoord.y * 2 * mpi + _Time[0] * 2) * 0.1;
 
        output.uv = TRANSFORM_TEX(dtexcoord, _MainTex);
 
        return output;
      }
 
      fixed4 frag (vertOutput input) : SV_Target
      {
        fixed4 col = tex2D(_MainTex, input.uv);
        return col;
      }
      ENDCG
    }
  }
}