CHAPTER 1 



INTRODUCTION TO THE TIJUANA RIVER 

 NATIONAL ESTUARINE RESEARCH RESERVE 



The story of Tijuana Estuary is complex. 

 Ecologically, it has been influenced by its 

 highly variable environment. Historically, it 

 has shifted from a natural to a highly modified 

 system. Politically, its fate has been hotly 

 debated, and competing interests continue to 

 influence its management. 



This is an attempt to synthesize and 

 interpret a growing data base on the estuary's 

 diverse biota -- its vegetation, algae, birds, 

 fishes, and invertebrates. Because so many 

 changes have occurred in response to 

 catastrophic events, we describe how each 

 aspect of the estuary appeared before 1980 

 and how it has responded to several 

 perturbations. The experimental tests of 

 these cause-effect relationships have not been 

 completed, and there is little reason to expect 

 that environmental conditions have stabilized 

 or that new types of disturbances won't occur. 

 Thus, this profile should be viewed as a stage 

 in the process of understanding Tijuana 

 Estuary. Like the estuary itself, our 

 knowledge is continuously evolving. 



1 . 1 THE INTERNATIONAL SETTING 



Tijuana Estuary is entirely within San 

 Diego County, California, although three- 

 fourths of its watershed is in Mexico (Figure 

 1.1). The Tijuana River originates in the 

 mountains of Baja California. Water from the 

 United States portion of its watershed flows 

 down Cottonwood Creek and joins the Tijuana 

 River in Mexico. The river then crosses the 

 border just north of the city of Tijuana, Baja 

 California. 



On old maps, Tijuana Estuary is called 

 Oneonta Lagoon or Slough. The Tijuana River, 

 which feeds it, has been variously called Rio 

 Tecate, Rio Tijuana, Tia Juana River, and 

 Tijuana River. In 1968, the U.S. Board on 

 Geographic Names approved the name Tijuana 

 River (D. Orth, Executive Secretary, U.S. 

 Board on Geographic Names, letter). 

 Somewhat later, the name Tijuana began to 

 replace Oneonta, but not everyone recognizes 

 it as an "estuary." Yet, is does fit the most 

 widely used definition, namely, "a semi- 

 enclosed coastal body of water" that is 

 "measurably diluted by fresh water..." 

 (Pritchard 1967). Because of its location as 

 the south-westernmost corner of the 

 continental United States, it has both national 

 and international significance. 



As discussed throughout this profile, the 

 estuary is very much a function of its 

 watershed. The land uses and management 

 practices on both sides of the border greatly 

 influence the quantity and quality of water 

 entering Tijuana Estuary. Thus, it is 

 important to characterize the regional 

 environmental conditions that have shaped and 

 continue to shape this international estuary 

 (Chapter 2 and Chapter 3, respectively). 



1 .2 ESTUARY TYPE CHARACTERIZATION 



Pritchard (1967) developed an estuarine 

 classification scheme based on geologic origin 

 and physiography. In this frame of reference, 

 Tijuana Estuary is very much like most of the 

 world's estuaries, because it is a flooded river 

 valley, also known as a coastal plain estuary. 

 As sea level rose during the last postglacial 



