Here are the local sites I could identify which related to the environment. First the major government and agency sites:
Climate Change Guyana - site of the government National Climate Committee. A new site with lots of information.
Environmental Protection Agency (EPA) - official government site. Good information about the EPA.
Guyana Energy Agency - official government site. Recently revised.
Guyana Forestry Commission - official government site. A main source for forestry info.
Guyana Geology and Mines Commission - official government site. A lot of info here.
Hydrometeorological Service of the Guyana Ministry of Agriculture - official government site. Includes climate change info and daily weather forecast.
Iwokrama International Rainforest Programme. Plenty of info about the rainforest, climate change and the programme. Recently updated.
Pesticide and Toxic Chemicals Control Board - official government site. Lots of info, updated in 2008.
And now a few other sites of interest:
ECO1 - local NGO
Guyana and the Environment. Some useful general info but not recently updated.
Guyana Marine Turtle Conservation Society. Info about their activities.