Something

struct VS_OUTPUT
{
	float2 TexCoords : TEXCOORD0;
	float4 Position : POSITION;
};

struct VS_INPUT
{
	float2 TexCoords : TEXCOORD0;
	float4 Position : POSITION;
};

float4x4 WorldViewProjection;

bool underWater = false;

Texture diffuseTexture;
sampler textureSampler = sampler_state 
{ 
	Texture = <diffuseTexture>; 
	magfilter = LINEAR; 
	minfilter = LINEAR; 
	mipfilter = LINEAR; 
};

VS_OUTPUT VS (VS_INPUT Input)
{
	VS_OUTPUT Output;

	Output.Position = mul(Input.Position, WorldViewProjection);
	
	Output.TexCoords = Input.TexCoords;
	
	return Output;
}

float4 PS (VS_OUTPUT Input) : COLOR
{
	if(underWater)
		clip(Input.Position.y);
		
    return tex2D(textureSampler, Input.TexCoords) + 0.3f;
}

technique Scene
{
    pass P0
    {
        VertexShader = compile vs_2_0 VS();     
        PixelShader = compile ps_2_0 PS();
    }
}