ZOAHARIAN.COM – An unusual sight occurred in the Cirata Reservoir area, precisely in Jangari, Cimanggu Village, Pasir Kawung, Cianjur Regency, West Java, Monday (28/9/2026).

Thousands of tilapia fish belonging to floating net cage farmers were found dead and floating around the reservoir waters. This condition emerged after the Cirata area was hit by heavy rain followed by strong winds, after previously experiencing a fairly long dry period.

The mass death of fish is thought to be related to the upwelling or umbalan phenomenon, namely the movement of water masses from the bottom layer towards the surface.

Footage circulating on social media via Samsul Bahri's Facebook account shows the surface of the water filled with floating fish. Before dying, a number of fish were said to be seen moving weakly and rising to the surface, as if they were having difficulty getting oxygen.

This condition is of concern to farmers because the appearance of large numbers of fish on the surface is not a common phenomenon.

Upwelling Can Change Water Conditions

The upwelling phenomenon occurs when water masses from the bottom of the reservoir move up to the surface. This movement can carry organic material and sediment that was previously in deeper layers.

These conditions have the potential to change the quality of the water around the cages, including the levels of dissolved oxygen (DO) which is very important for fish life.

Sudden changes in weather after a long dry season can be one of the conditions that trigger changes in the water layer. Heavy rain, temperature changes and strong winds can strengthen the process of mixing water masses in the reservoir.

If water masses from the bottom that have low oxygen levels rise to the surface, the fish around the cage can experience stress due to reduced oxygen available.

One of the symptoms can be seen from the behavior of fish that move abnormally, congregate on the surface, appear weak, and eventually die if the condition lasts long enough.

Cultivators Threatened with Loss

The mass death of fish in Jangari is not just a problem for the aquatic environment. For cultivators, this incident also has the potential to cause economic losses.

Fish that die before entering the harvest period means that the capital that has been spent to buy seeds, feed, maintain cages, and during cultivation is in danger of being lost.

Cirata Reservoir itself is one of the areas that is widely used by the community for cultivating fish using a floating net cage system. Therefore, sudden changes in water quality can have a direct impact on cultivation activities.

A number of previous studies regarding fish deaths in the Cirata Reservoir have also discussed the phenomenon of upwelling and its relation to changes in dissolved oxygen levels.

Need Water Quality Check

Although the upwelling phenomenon is thought to be one of the causes, the exact cause of mass fish deaths needs to be ascertained through examining water conditions.

Data collection on the number of fish that died and the value of farmers' losses is also needed to find out how big the impact of the incident was.

It is important to check water quality, especially temperature, dissolved oxygen levels and other parameters, after heavy rain and strong winds hit the Cirata Reservoir area.

Changes in water conditions can occur relatively quickly. For cage farmers in Jangari, this phenomenon is a reminder that changes in extreme weather and reservoir water dynamics can have a big impact on the sustainability of fish farming.