Feature summary (what you would like to be able to do and where):
The map could show health-related data about the environment. For example, I'd like to know if a lake's water quality is certainly unsuitable for swimming.

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):

• See this map of PFAS pollution of waters in Europe; sth like it also exists for the U.S.; this is useful for seeing if a lake has fish that are safe to eat (note that for rivers it would be good if it was possible to tab on the river at any spot of it which shows the Wikipedia article for the river as well as spot-related information such as pollution measurements)
• One could use to see if there is data on the chemical and other pollution of a river or lake and if so, if it's likely a good personal choice to swim in it (if available at all, such data is all dispersed and hard to find)
• To see average air pollution levels of a city or at a certain time (this would cover a region of the map, not just a particular spot)
• At some point this could also be used to identify blind-spots of e.g. pollution entry to rivers/oceans as well as key sites that for example would benefit from better monitoring or set up of trash-bins

Benefits (why should this be implemented?):
These are described in the use-cases. For example: better public health and environmental education and awareness as well as better integration of environmental data with Wikidata and Wikipedia. It could also motivate users to set up their own sensor systems to enable Public monitoring of environmental determinants of health providing better-quality and more extensive open data on this.

Maybe there could be subtasks per type – showing some info on water quality of lakes would probably be much easier to implement than quickly changing region-covering air pollution data. While it may require some additions to Wikidata for example and is not easy to implement, the societal value of this could be enormous (for example every year millions of people die from air pollution and chemical pollution of rivers and more basically one of the most transgressed planetary boundaries) and advances the open knowledge system to be much more relevant and useful in practice for people in the real world.