Aboriginal peoples in many parts of the world have developed ways of monitoring, amassing information, understanding and making associations about the local ecosystems they depend upon for subsistence resources. Appropriately, using their Traditional Ecological Knowledge (TEK), and ecosystem monitoring expertise may facilitate sustainable ecological systems. Systematic ecosystem monitoring is incidental to the sustainability of local ecosystem integrity and health. In areas disturbed by significant industrial, land and resource development, the capacity to "monitor" changing ecosystem conditions is crucial. This research demonstrates how five Aboriginal (Cree) communities in northern Alberta, Canada incorporate "systematic" ecosystem monitoring elements to assess local ecosystem condition and changes. The systematic ecosystem monitoring elements are described, including the use of "cultural keystone species" as condition indicators, the diagnostic measures used, the temporal and spatial elements, and how Cree Land Based Experts interpret and make associations about the health of fish, wildlife, plants, landscape habitat, water and air. This research reports on the observations of populations and condition of a number of cultural keystone species, hydrological yield and quality, and critical wildlife habitat affected by the cumulative effects of forestry, oil and gas, and a contaminant treatment facility development in the study area. The work also discusses the implications and ramifications to local Cree people to these changing ecological conditions. Finally, this research suggests how local Aboriginal peoples, their Traditional Ecological Knowledge (TEK), and their ecosystem monitoring expertise, can be of applied use within ecosystem management, and cumulative effects frameworks.