Hydropower entered July 2026 as Southeast Europe’s most important flexible renewable resource—and one of its most constrained. Prolonged heat and drought reduced river flows and generation in several major markets just as cooling demand was increasing and solar-heavy power systems needed dispatchable electricity after sunset.
The consequence is more complex than a simple loss of renewable megawatt-hours. When hydro conditions deteriorate, the region loses both energy volume and operational flexibility. Gas, coal, imports and storage must replace not only the electricity that hydropower would have generated, but also its ability to respond rapidly during evening peaks and periods of system stress.
July’s water conditions became a regional electricity-market variable. The most visible physical signal came from the Danube. Romanian water levels fell to their lowest since 1996, with river flow at the country’s entry point measured at approximately 1,700 cubic metres per second, compared with a July average of around 4,700 cubic metres per second. The low water affected irrigation, ferry services, grain shipping and tourism, while authorities managed reservoirs partly to safeguard nuclear cooling requirements.
The deterioration in the power sector had already appeared in weekly generation data. Regional hydropower output fell 4.7% to 3.57 TWh during Week 25, with reductions in Italy, Bulgaria and Romania. During the same period, regional electricity demand rose 3.1%, thermal generation increased 19.4%, and gas-fired output rose 32.3%.
Hydro production then declined by a further 2.8% week on week to 3.51 TWh during Week 26. Türkiye’s output fell 5.9%, removing 142 GWh from the regional total, while Bulgarian hydropower generation dropped 44.6%. Serbia, Croatia and Greece moved in the opposite direction, although some of their percentage increases reflected recovery from comparatively low previous levels.
A July 10 daily snapshot showed hydro output falling by approximately 520 MW to 4,871 MW, even as regional demand reached 31,291 MW. Gas, coal and nuclear collectively supplied substantially more electricity than hydropower on that day, highlighting how quickly lower water availability can shift the generation mix toward thermal and other firm sources.
These figures do not mean that every Southeast European river basin was uniformly dry or that current river flow translates directly into the output of every hydropower plant. Reservoir storage, local rainfall, plant design, operator strategy and cross-border obligations all matter. The uneven national results confirm that regional averages can conceal substantial differences between individual systems.
Hydropower’s value is increasingly being determined by timing rather than volume alone. In a solar-heavy electricity market, the most valuable feature of reservoir hydropower is not necessarily the amount of electricity it produces over 24 hours. It is the operator’s ability to retain water during low-price periods and generate when solar output declines, demand remains elevated and neighboring markets are also seeking imports.
This creates an apparent paradox. Dry conditions can increase the market value of each dispatchable hydro megawatt-hour while reducing the number of megawatt-hours available for sale. A generator may capture higher peak prices while recording lower total production and facing greater uncertainty over future reservoir levels.
The distinction between plant types is therefore critical. Run-of-river facilities are closely exposed to immediate river flows and have limited ability to choose when they generate. Reservoir plants can shift output across hours, days or seasons, subject to water levels and downstream obligations. Pumped-storage facilities can arbitrage electricity prices, but they consume more electricity while pumping than they later return and do not create additional water or net energy.
When water is scarce, an operator may conserve reservoirs for evening peaks, system reserves or later seasonal needs. That behavior is economically rational, but it can also make off-peak electricity scarcer and widen intraday price spreads.
The region is losing a hedge against both gas prices and electricity imports. Hydropower normally limits the number of hours in which gas-fired generation becomes marginal. When hydro output weakens, gas plants are called more frequently, particularly during the evening transition from strong photovoltaic production to peak residential and cooling demand.
Week 26 demonstrated this effect. Lower hydro availability made Greece, Romania, Serbia and neighboring markets more dependent on thermal generation and cross-border supply. Bulgaria remained a major exporter, but other domestic generation had to compensate for its sharp hydro decline while still supporting export commitments.
This linkage becomes particularly important when gas prices are rising. A hydro shortfall during a low-gas-price period may be manageable. The same shortfall when European gas approaches €60/MWh can have a much larger impact on wholesale electricity prices because the replacement generator carries a substantially higher fuel cost.
Hydropower is therefore more than a renewable-generation category. It is also a financial hedge against fuel-price volatility, carbon exposure, imports and transmission congestion. The value of that hedge rises precisely when the available water behind it is becoming more limited.
Water allocation is becoming an energy-policy issue. July’s Danube conditions exposed the growing competition among energy and non-energy users. The same water system supports conventional hydropower, pumped storage, nuclear cooling, agriculture, freight transport, tourism, ecosystems and community water needs.
That creates significant policy and contractual complexity. Maximizing short-term electricity production may conflict with maintaining navigation depths, irrigation supplies, ecological flows or cooling reserves. On cross-border rivers, upstream decisions can also influence downstream generation and water availability.
Hydropower valuations therefore need to incorporate more than historic production averages. Investors should assess water-management rules, bilateral treaties, climate scenarios, environmental constraints and the priority assigned to competing uses during drought. A plant’s installed capacity may remain unchanged while its dependable summer energy output falls substantially.
Pumped storage is moving toward the center of the regional investment agenda. The most important July project signal was the renewed Serbia-Romania initiative for Iron Gate III, known in Serbia as Đerdap 3. The two governments signed a memorandum on July 16 to exchange information and assess the potential joint pumped-storage project upstream of the existing Iron Gate I complex. Serbia also plans to begin spatial-planning and technical-documentation work during 2026.
The project’s final configuration, number of units, installed capacity and reservoir size have not yet been determined. Those parameters are expected to be defined through feasibility work and a front-end engineering and design phase expected to last 36 months. A preliminary completion objective of 2036 has been reported, alongside an indicative investment estimate exceeding €2.63 billion, although both cost and timetable remain subject to further studies.
The commercial rationale is strong. Existing Iron Gate I and II facilities have combined capacity above 2,800 MW. Adding pumped storage could allow the system to absorb low-priced midday solar electricity and release it during evening peaks, winter scarcity or strong export demand. It could also provide reserves, balancing services and renewable-firming products across Serbia, Romania, Bulgaria and Hungary.
However, the project should not yet be valued as committed capacity. Bilateral water governance, environmental studies, hydrological modelling, financing, transmission upgrades and the treatment of impacts on existing Danube plants remain unresolved. The July memorandum advances cooperation and coordination; it is not a final investment decision.
Modernizing existing hydropower assets may outperform greenfield development in the near term. Southeast Europe’s need for flexibility supports additional pumped storage, but the most attractive investments may be less dramatic. Turbine refurbishment, efficiency improvements, digitalized reservoir dispatch, capacity uprates and pumping capability between established reservoirs can deliver significant benefits with lower permitting and environmental risk than a new large dam.
Existing sites also tend to possess grid connections and established water rights. Those advantages are becoming increasingly valuable as new infrastructure faces longer environmental reviews, stronger public scrutiny and more complex cross-border obligations.
Greenfield hydropower remains possible, particularly where energy storage, flood control and broader water-management benefits can be combined. Nevertheless, headline installed capacity alone is no longer an adequate measure of project value. The more relevant metric is dependable flexible output under realistic dry-year conditions.
The region may have less hydropower energy available, but the flexibility that remains is becoming more valuable. Hydropower will remain central to Southeast European electricity markets, but its role is changing. In wet periods, it supplies large volumes of relatively low-cost renewable electricity. In dry periods, it becomes a limited strategic reserve that operators must allocate across the highest-value hours and essential water uses.
For the remainder of summer 2026, market participants will need to monitor rainfall, reservoir trajectories, river flows and operator dispatch, rather than simply installed hydropower capacity. Continued drought would reinforce evening power premiums, gas consumption and import requirements. Meaningful rainfall could reverse the balance comparatively quickly, particularly in systems with substantial reservoir storage.
The long-term investment message is equally clear: hydropower must increasingly be assessed as climate-exposed infrastructure. Projects capable of storing energy, operating flexibly and functioning across a wider range of hydrological conditions will command a premium over assets whose economics depend heavily on historical average inflows. In Southeast Europe, the value of hydropower is increasingly shifting from the number of megawatts installed to how reliably those megawatts can be delivered when the system needs them most.
