The physical, chemical, and biological structure of permanently stratified lakes have analogy to the Earth’s Precambrian oceans. Both have deep waters devoid of oxygen, have lower sulfur contents than the modern ocean, and have biogeochemical cycles predominantly driven by microbes. Through two stratified and iron-rich lakes in Minnesota and Michigan, my group is studying the significance of iron-based photosynthesis in primary productivity and its potential biosignatures, methane production, consumption and export in iron-rich (i.e. ferruginous) waters, as well as primary and diagenetic mineral and isotopic signatures of these systems that are recorded in sediments. While our findings are relevant to Precambrian biogeochemistry, I will present evidence that these small, stratified ferruginous lakes might be fairly common in the Midwest, and perhaps are becoming more so. Therefore, our findings from monitoring these two lakes are also relevant to trends in our region’s water quality, and the contribution of similar lakes to global greenhouse gas, nutrient, and metal cycles.