For C# there exist many wrappers that offer an interface to communicate with OpenCL.
https://openclnet.codeplex.com/
The short-term goal is providing an easy-to-use abstract layer which provides access to the full capability of OpenCL without sacrificing performance.
https://github.com/tunnelvisionlabs/NOpenCL
Cloo is an open source, easy to use, managed library which enables .NET/Mono applications to take full advantage of the OpenCL framework.
https://sourceforge.net/projects/cloo/