the area." (F.S. Chapter 373.042, Munson et al. 2005). What constitutes "significant harm" was

not defined. The District has identified loss of flows associated with fish passage and

maximization of stream bottom habitat exposure as significantly harmful to river ecosystems.

Significant harm can also be defined as quantifiable reductions in the amount of available habitat

(Gore et al. 2002).

 Determining the amount of habitat loss, or deviation from a benchmark, that a system is

capable of withstanding is based on professional judgment. In establishing MFLs, the

SWFWMD recognized that the Instream Flow Incremental Methodology (IFIM) involves a

negotiated threshold to be used as an acceptable measure of habitat loss (Bovee et al. 1998).

Gore et al. (2002) note that instream flow analysts often consider a loss of more than 15%

habitat, as compared to undisturbed or current conditions, to be a significant impact on a

population or assemblage when employing Physical Habitat Simulation (PHABSIM) analysis.

With some exceptions (e.g., loss of fish passage or wetted perimeter inflection point), there are

few clearly delineated break points which can be relied upon to judge when significant harm"

occurs. Hill and Cichra (2002) noted that loss of habitat in many cases occurs incrementally as

flows decline, often without a clear inflection point or threshold.

 The District employed a threshold of a 15% change in habitat availability as a measure of

significant harm for the purpose of MFL development. Although the District utilized a 15%

change in habitat availability as a measure of unacceptable loss, percentage changes employed

for other instream flow determinations have ranged from 10% to 33%. For example, in reference

to the use of PHAB SIM, Dunbar et al. (1998) noted that an alternative approach is to select a

flow that provides protection to 80% of the habitat, which is equivalent to a 20% loss. Jowett

(1993) used a guideline of one-third loss of existing habitat at naturally occurring low flows, but