So what do you think is happening in Strangerville?

I think it's alien plant species that release spores and Sims get infected by the air if too close to those alien pod plants and create pod people/Sims. I also agree the plants could taint water with infection too or just attack people. I think the SIM government knew about this plant life, tried to use them for their own gain. I believe this led the plants to strike back. Now SIM government wants to try to cover up, lol.