This scene was created initially by taking the water scene I had already created, and editing it to the shape of a lake and making the texture a bit more distorted and ripply. Then I began by creating the trees.
Trees - These were created entirely from my own shapes. I started off by making a long, thin cylinder and then putting a cone on top. Frankly, this didn't look convincing at all. Then I used the 'Convert To Editable Mesh' tool when you right click the image. Then, by altering the spots on the mesh, created a distorted version of the cone. To make it more realistic I took an image of a tree's leaves and applied it as a material through the material editor. Then copied the cone shape 3 times to created more branches and a bushier tree. To finish, I then copied the tree many times and scattered them around the lake.
Snow - This was created by making another plane which was bigger than the lake. Then I edited the material this was on by making it similar to the lake but without the reflection tool. I then changed the colours to pure white and gave it shadows by changing the ambient colour to black.
Lights - The lights were created from an omni light, reached from the create>lights>omni tools. I then selected 'On' for shadows, and placed it on the workspace. I then moved it in a suitable position so that it would give the trees shadows ontop of each other and highlight the features of the snow material.
Sky - The sky was done by creating the whole image inside a dome, which then had a material applied to the inside of it. The enviroment colour was initially set to a pale blue colour, so now all I needed to add was the clouds and texture. To do this, I made a material which was completely white, but in the 'Opacity' field on the maps drop down menu, I chose 'Noise' meaning the sky would only show parts of the background colour through it. I then changed the noise style to Turbulence to make it more patchy. Then I altered the other options like tiling and noise threshold to give the best results. Finally, to add the fading background to the sky, I duplicated the dome, and made it slightly larger. Then I changed the material to a new one, on which I changed the 'Opacity' map to 'Gradient' so the white parts of the sky will be stronger in the distance, like in the real sky.
Here is the result: