Ecological ponds can be a good teaching tool for science teachers, but they must be built and maintained properly to provide students with a safe and suitable learning environment. However, many schools do not have the ability to build and maintain an ecological pond. This study used virtual reality technology to develop a web-based virtual ecological pond, supported by situated learning theory and the instructional design of "Aquatic Life" learning unit. Elementary students can explore in the virtual ecological pond to observe aquatic plants and animals for obtaining important concepts of aquatic ecology. A teaching experiment was conducted to investigate the learning effectiveness of this instructional design, and the results showed that using the virtual ecological pond could improve students' critical-thinking ability. Most students found the virtual ecological pond interesting and easy to use, so it is helpful to learning aquatic life and ecological conservation. (Contains 6 figures and 5 tables.)