500 BC
 Earliest known masonry architecture at Piedras Negras.
AD 359
The earliest known ruler at Yaxchilán, Yoaat B’alam I is in power.
460
 The earliest known ruler at Piedras Negras, Ruler A, is in power

600-
800

600 The rulers of Piedras Negras and Yaxchilán are at the height of their powers, and often at odds with one another. Artists at these sites produce some of the finest pre-Columbian stonework.
700
Peak of Mayan population in Usumacinta region, with estimates ranging as high as 2 million people for the river basin.
795
 Last dated monument at Piedras Negras.
808
 Last date recorded on monuments at Yaxchilán.
900
 The Collapse of “Classic” Mayan Civilization in the area. Small populations continued to live in the areas around Piedras Negras and Yaxchilán. Lacandón Mayas venerate these locations well into the 20th-century.
1524
 Cortés marches through the Usumacinta Valley on his way to Honduras.
1821
 Mexico and the Central American Republic declare their independence from Spain.
1840
 The Central American Republic is dissolved, and Guatemala becomes an independent state.
1883
 Alfred Maudslay is the first to describe Yaxchilán in print.
1892
 Ludovic Chambon is the first to describe Piedras Negras in print.
1917
 Mexican Constitution declares water a national property which can only be used through due authorization by a Federal Authority
1946
 Mexican Ministry of Water Resources was established and put the responsibility for water development within the realm of a single organization.
1949
 Stream gage installed on the Rio Usumacinta at Boca del Cerro, Mexico
1961
 International Commission on Limits and Waters between Mexico and Guatemala was formally established by exchange of diplomatic notes between the countries. Commission has authority to advise the two countries on border issues and the equitable use of water.
1972
 Mexican environmental regulations and Federal Water Act were enacted to reinforce the legal framework for water management by defining regulations and controls for water use and water allocation priorities.
1976
 First Mexican National Water Plan was completed and the National Water Plan Commission was created to implement the plan.
1980
 The International Commission on Limits and Waters between Mexico and
Guatemala authorizes studies on the hydrologic and agricultural potential of the Usumacinta river basin.
1980s & 1990s
 The Sierra del Lacandón National park becomes a refuge for members of the
Comunidades de Poblaciones en Resistencia del Petén (CPR-P).
1985
 The Chixoy Hydroelectric Dam is completed and capable of generating 300 MW of electricity. The project, built between 1976-1985 by the Guatemalan National Electrification Institute was financed with loans from the World Bank and the Inter-American Development Bank. Engineering studies started in 1972 and construction began in 1976. However, several designed changes were made to adjust for a severe earthquake in 1976 and extensive karsts cavities and complex subsurface geology that were encountered. In 1996 the World Bank President described the project as very week on technical and economic grounds (Levy 2002).
1988
 Mexico and Guatemala ratified a convention for protecting the border environment. The agreement requires both countries to evaluate effects of proposed activities within the boundary zone.
1989
 Presidential Decree created the National Water Commission of Mexico. The Commission was established as an autonomous federal authority dealing with water management and is responsible for coordinating investment programs and setting priorities and constraints based on the actual situation in each of the countries rivers basins.
1990
 Agreement between Mexico and Guatemala was signed giving treaty status to the International Commission on Limits and Waters between Mexico and Guatemala.
1990 Creation of the Maya Biosphere Reserve, including the Sierra del Lacandón
National Park (Parque Nacional Sierra del Lacandón)
1991
 Plans to build a series of traditional style hydroelectric dams on the Rio Usumacinta near the Sierra del Lacandón National Park were postponed. During the planning process Mexican hydrologists at the Mexican Institute of Hydrology recommended installing a series of in-stream turbines instead of large dams. However, plans for both types of hydroelectric systems were postponed.
1992
 Mexican National Water Law was enacted and a Public Registry of Water Rights established. The National Water law explicitly declares sustainable development as its primary objective and requires that a license or concession from the National Water Commission is needed to use the Nation’s waters. The law also requires that those who benefit from water abstraction or waste discharge must contribute to resource management and water quality restoration and improvement in proportion to their consumption.
1994
 Zapatista Liberation Army, a predominately indigenous group based in the region, fought the Mexican Federal Army for 11 days in opposition to NAFTA and other government policies.
1994-1996
 The Government of Guatemala and representatives of the URNG--an umbrella organization of four insurgency movements--signed a number of accords, which brought to a close a 36-year long internal conflict, the longest in Latin America. Six of the accords are "substantive." Others focus on procedural matters.
1996
 Settlers from the Comunidades de Poblaciones en Resistencia del Petén are moved from the Sierra del Lacandón National Park and resettled in new communities outside Park’s boundaries.
1997
 Guatemala adopts the General Electricity Law and the Ministry of Energy and Mines is entrusted with enforcing the law, which includes regulations on hydropower reservoirs.
1999
 Guatemalan government sells 80% of the assets of the Guatemalan Power Authority and continued the process of privatization of the electrical distribution system.
2000
 World Commission on Dams completed a review of large dams and concluded that successful dams require multi-year, multi-disciplinary studies.
2002
 A new hydroelectric dam on the Usumancinta at Boca del Cerro is proposed as part of the Tercer Milenio project of the Mexican Government and Regional Plan Puebla-Panama project of the Interamerican Development Bank. This dam would be an integral part of a larger irrigation and hydropower system (www.mexicotm.com).
2002
 Feb 21, 2002. At a press conference with Mexican President Vincente Fox, Guatemalan President Alfonso Portillo acknowledges the Usumancinta hydropower potential and ecological importance and states:

“la potencialidad hidrológica que tiene el sur de Méxi co, del Río Usumacinta, del Río Suchiate, que compartimos tiene una potencialidad para darle energía no sólo a Centroamérica y a México, ya sabemos que tenemos todavía déficit en energía, sobre todo en Guatemala y algunos países de Centroamérica. Este es un proyecto muy ambicioso. Sé que esto implica hacer estudios más serios, porque tiene que ver con el medio ambiente, la conservación del equilibrio ecológico, etcétera, pero hay grandes posibilidades”. (www.presidencia.gob.mx)
2002
 Two dams burst in central Mexico killing 14 people and affecting 4500.
2003
 A massive fish kill on a tributary of the Motagua river in Guatemala was linked to the January 8th flushing of the Las Vacas hydroelectric reservoir. A similar fish kill was reported when the reservoir was flushed in February 2002.

 

`