Fishes inhabiting streams and rivers in the interior of North America experience a continental climate. Water temperatures reach 0 °C in winter and are high in summer. There is a marked seasonal cycle in discharge. These circumstances make groundwater a crucial component of river habitats. Groundwater can influence the distribution, reproductive success, biomass and productivity, behaviour and movements of fishes, and is especially important in winter and summer. Winter flows are minimal and are affected by ice. In winter, the importance of groundwater increases northwards. Groundwater provides overwintering habitat free of subsurface ice and fish may migrate long distances to take advantage of it. The melt season can account for up to half the annual discharge. In summer, groundwater is important for maintaining discharge and moderating stream temperatures. During critically hot weather, groundwater refugia protect species exposed to temperatures approaching their thermal limits. Since groundwater exerts such an important influence on river habitats, its quality, quantity and sustainability should be considered before development proposals are approved which could alter it. Examples of the role of groundwater in the ecology of some species show how localised and critical habitats influenced by groundwater can be, and, in consequence, how necessary it is to protect them. Protection is complicated because groundwater distribution pathways are often unknown and recharge areas may be remote from discharges. Scale becomes important in identifying potential risks to critical stream habitats from all types of landscape modification and water abstraction. Groundwater temperatures reflect mean annual air temperatures and are likely to change as global climates respond to increases in the greenhouse gases in the atmosphere. This could profoundly change critical fish habitats, particularly those at the margins of species distributions or those that are already overcrowded. Such considerations emphasise the importance of developing proper strategies for the conservation of groundwater. Copyright © 1999 John Wiley & Sons, Ltd.

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The context in which water resources management operates continues to expand as governance regimes are recognized as polycentric in structure and institutions are more broadly interpreted. This paper explores the "expanded" institutional context for water resources management. Institutions of water resources management in Ontario are presented and a chronology of management in the Grand River watershed is detailed to illustrate the breadth and depth of institutions in practice. Examining the institutional context of the Grand River watershed confi rms the shift in governance, affi rms the merits of broadly understanding institutions and recognizes their polycentric nature. The article closes by considering the implications to the nested-basin approach of water resources management. Résumé : Le contexte dans lequel la direction des ressources des eaux fonctionne continue à développer selon qu'on reconnaît les régimes de gouvernance comme "polycentric" en structure et que les institutions sont plus entièrement interprétées. Cette étude examine le contexte institutionnel "expantionel" pour la direction des ressources des eaux. Les institutions de la direction des ressources des eaux en Ontario sont présentées succinctement et une chronique de la direction dans la ligne de partage des eaux (watershed) de Grand River est détaillée pour illustrer la largeur et la profondeur des institutions qui existent aujourd'hui. En examinant les contextes institutionnels de la ligne de partage de Grand River, on peut confi rmer le changement de gouvernance, le mérite de comprendre en gros les institutions et la reconnaissance de leur nature "polycentric". Cette étude fi nit par considérer les implications à l'approche "nested-basin" de la direction des ressources des eaux.

High‐resolution velocity measurements were taken over a series of redds on a gravel‐bed stream using a Pulse Coherent Acoustic Doppler Profiler (PCADP) to quantify the hydrodynamics of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) redds. On redds studied, over 4500 velocity measurements per redd were acquired per day to quantify the flow velocity, flow depth and related fluid mechanics metrics of Reynolds numbers, Froude numbers and turbulent kinetic energy per unit area. Results showed that velocity and Froude numbers varied widely at the redd scale, but consistently showed higher velocities and Froude numbers over the tailspill regions relative to the surrounding study limits. Results of Reynolds numbers calculations showed no apparent correlations to spawning location preference and redd structure. Turbulent kinetic energy per unit area consistently demonstrated a strong correlation with redd locations. The metric maintained low values (i.e. unidirectional flow with little turbulence) where all redds and attempted redds were observed. The study also demonstrates that a number of hydraulic metrics and several spatial scales will likely be necessary to understand any inherent relationship between river hydraulics and redd placement. Copyright © 2010 John Wiley & Sons, Ltd.