What significant issue was highlighted in scientific surveys in 2005?

The significant issue highlighted in scientific surveys in 2005 was the population crash of native fish. This event underscored the critical environmental challenges facing California's aquatic ecosystems, particularly the decline of native species such as salmon and delta smelt. The surveys revealed that overfishing, habitat loss, and the impact of water management practices were contributing to a dramatic decrease in these populations.

Understanding the plight of native fish is crucial because these species are indicators of the overall health of aquatic ecosystems. Their decline not only affects biodiversity but also reflects deeper issues in water management and environmental conditions in California's water systems. Restoration efforts for these fish often become central to water policy discussions, as maintaining healthy populations requires careful consideration of water allocation, habitat restoration, and pollution control.