Urban wetlands are one of the important natural resources in cities and have an essential role in the sustainability of the urban environment. They offer various ecosystem services in cities, for example, by mitigating the risk of floods, providing water purification, groundwater regulation, and biodiversity promotion. Urban wetlands also provide recreational opportunities such as swimming and boating, that improve citizens’ well-being. Unfortunately, human activities and environmental factors have been the primary reasons that have destroyed urban wetlands. To identify the main factors which threaten wetlands, as a case study, we investigated the environmental history of six urban wetlands in Helsinki starting from 19th century to the present. We collected historical information from available documents such as research articles, technical reports, maps, and photos, and then we compared the past situation of these urban wetlands with the current conditions throughout history. We also support our statements by referring to urban wetlands with similar conditions from different continents to explain the reasons for wetlands’ disappearance, degradation, or survival. We show that population growth, land-use change, and climate change have been the main threats that have caused the degradation and even the loss of urban wetlands. We discuss the influencing factors which threaten urban wetlands and we highlight the role of policy and decision-makers in the rehabilitation and maintenance of urban wetlands.