Study region
Gatun Lake, Panama Canal, Republic of Panama.

Study focus
The Panama Canal expansion, which was completed in June 2016, included the construction of new locks, known as Neo-Panamax, which are 3.3 times larger in volume than the old locks, known as Panamax. Water quality measurements of Gatun Lake, the main lake of the Panama Canal, are available, at different temporal scales, for the periods before and after the expansion. However, a statistical analysis of the salinity data has not been made available to the scientific community. This study quantifies spatiotemporal variations in salinity concentrations of Gatun Lake before and after the expansion of the Panama Canal, and examines their interaction with lake water levels and El Niño Southern Oscillation (ENSO) cycles. To achieve this, summary statistics, trend analyses and interpolation methods were applied to the available salinity and water level data for Gatun Lake.

New hydrological insights for the region
Before the expansion of the Panama Canal, average salinity in Gatun Lake was < 0.05 Practical Salinity Units (PSU). After the expansion, average salinity is 0.21 PSU, which represents an increase of over four times. In Gatun Lake salinity has been observed to be the highest near the Neo-Panamax locks, averaging 0.6 and 0.5 PSU after the expansion near Agua Clara locks in the Atlantic and Cocolí locks in the Pacific, respectively. After the expansion, salinity in Culebra Cut, the narrowest part of the Panama Canal, is about 0.1 PSU. This study concludes that average salinity in Gatun Lake is weakly anti-correlated to its water level and it responds to changes in water level with a delay of one to two months. In June 2020, at the end of a strong El Niño period, average salinity in Gatun Lake reached its peak of 0.39 ± 0.19 PSU, only one month after the lake’s water level reached its second lowest level in the past decade (24.5 m). During El Niño events, salinity showcases a statistically significant increasing trend whereas during La Niña events no significant trend could be identified.

Gatun Lake, located in the Panama Canal Watershed (PCW), is the main source of freshwater for the Canal's operations and it provides drinking water for nearly 600,000 people, which represents roughly 15% of the country's population. Since its creation at the beginning of the 20th century, Gatun Lake has slowly been transitioning from a swamp environment to a more saline-governed ecosystem. However, since the completion of the Canal's expansion project and inauguration of the Neo-Panamax locks in 2016, salinity in the lake has been increasing at a faster pace. The progressive salinization of this water body is not only a concern from the perspective of drinking water supply and human health, but for the lake's biodiversity as well. In order to understand the magnitude of this issue, evaluate the impact of climate change and design effective mitigation and management strategies, robust modelling tools are required. Nevertheless, these tools often require high volumes of high-quality data that are not always readily available. This paper illustrates the characterization of Gatun Lake's hydrodynamic behaviour and water quality condition using a numerical model built with Delft3D and publicly available open data, which includes bathymetry from GEBCO and hydrodynamic data from ACP's AQUARIUS web portal. Although further refinement of the model is still required, overall, it was demonstrated that reasonably good results can be obtained through a model built using publicly available open data.