ASP.NET WebApi - Multiple GET actions in one controller

I have Users controller and basic REST pattern is working just fine. However I need one additional pattern users/{id}/usergroups that will return all user groups for that user.

What would be the best way to implement this since I imagine I will need similar routes on many more controllers. Just default ones are not enough...

Error

Multiple actions were found that match the request: Api.Models.Users.User GetUser(Int32) on type Api.Controllers.UsersController System.Collections.Generic.IEnumerable`1[Api.Models.Users.UserGroup] GetUserGroups(Int32) on type Api.Controllers.UsersController

Code

// GET api/Users
public IEnumerable<User> GetUsers()

// GET api/Users/5
public User GetUser(int id) // THIS IS CONFLICT 1

// PUT api/Users/5
public HttpResponseMessage PutUser(int id, User user)

// POST api/Users
public HttpResponseMessage PostUser(User user)

// DELETE api/Users/5
public HttpResponseMessage DeleteUser(int id)

// GET api/Users/5/UserGroups
public IEnumerable<UserGroup> GetUserGroups(int id)  // THIS IS CONFLICT 2

Edit 1

I did what amhed suggested and it doesn't solve the issue.

// GET api/Users/5
[HttpGet, ActionName("getuser")]
public User GetUser(int id) // THIS STILL DOES NOT WORK

// GET api/Users/5/UserGroups
[HttpGet, ActionName("usergroups")]
public IEnumerable<UserGroup> GetUserGroups(int id) // THIS WORKS

// ROUTES
config.Routes.MapHttpRoute(
    name: "DefaultApi",
    routeTemplate: "{controller}/{id}/{action}",
    defaults: new { id = RouteParameter.Optional, action = RouteParameter.Optional }
);