Identify a major threat to freshwater biodiversity.

Habitat alteration is a major threat to freshwater biodiversity because it directly impacts the ecosystems that support a wide variety of flora and fauna. Freshwater habitats, such as rivers, lakes, and wetlands, often undergo significant changes due to human activities, including urban development, agriculture, and dam construction. These alterations can lead to loss of spawning sites, decreased water quality, and changes in sediment flow, which fundamentally disrupt the delicate balance of these ecosystems.

When habitats are modified, the native species that depend on those environments often struggle to survive due to the loss of their natural homes and resources, making them more susceptible to extinction. Moreover, altered habitats can facilitate the invasion of non-native species, which can further exacerbate the decline of native biodiversity. As a result, habitat alteration not only affects the immediate physical environment but also has cascading effects on the species that inhabit these aquatic ecosystems, thereby leading to a substantial decline in freshwater biodiversity overall.

In comparison, while overfishing, climate change, and the introduction of non-native species also pose significant threats to freshwater ecosystems, the direct impact of habitat alteration makes it a leading cause of biodiversity loss in these environments.