Protecting Aquatic Vegetation

Road works in general and stream crossing in particular can have a number of impacts of aquatic habitat. These impacts need to be considered in all phases of road work, from initial route selection to maintenance and deactivation. Impacts can include changes in channel characteristics, sediment loads, loss of riparian vegetation, or even direct mortality of eggs and small fish.

Salmon, trout, and other freshwater speces are found in streams, lakes, and, in some cases, wetlands. Fish are extremely sensitive to habitat degradation. Trout and salmon in fresh water need clean, stable gravel for spawning and egg incubation, food, well-oxygenated water, and a variety of stream, lake and wetland habitats to support different life stages and provide protection from predators and stream flow extremes, both high and low.


Streamside vegetation contributes to fish habitat in many ways: providing cover, stabilizing streambeds, moderating temperatures, providing food; and providing nutrients to aquatic organisms. Large organic debris in the stream channel provides channel stability, protection from predators, moderation of stream flows, and helps create complex habitats. These stream areas also provide permanent homes, resting areas, and movement corridors for wildlife.


Fish primarily eat insects. These insects may originat from the stream itself, or they may fall from streamside vegetation into the water. Terrestrial vegetation (leaves, etc.), and aquatic plant material and algae play akey roles in supporting food-producing processes in the stream ecosystems.


Stable, silt-free gravel beds are essential for successful salmon and trout spawning and egg survival. Spawning beds may be degraded or destroyed as a result of extreme flows, excessive erosion, sedimentation, and changes in channel definition.

Water Quality

Fish are particularly senstive to changes in water quality, temperature and oxygen levels. Suspended sediments can abrad or clog gill filaments and reduce visibility of insects, thus reducing feeding success. As well, the presence of contaminants or toxins, even if they are not directly responsible for fish kills, can reduce the vigour of fish, increasing losses to predators or disease.

Water Flows

The state of water, whether stagnant or in motion, also plays a key role in affecting water temperature. Flow energy is a major factor in the transport, sorting and deposit of the various materials that can be found in a waterway, from nutritious sediment to minerals, gravel, and boulders.

Stable stream hydrology is necessary to maintain healthy fish populations. Major flooding can destabilize streambanks and impact critical habitat, degrade water quality by contributing sediments and damage or destroy spawning beds by cutting off oxygen supply to the eggs. Low flows reduce available habitat and can isolate fish into pools, exposing them to excessive temperatures and predators.


Salmon are genetically programmed to return to spawn in the streams from which they originated. Barriers to access, such as improperly designed culverts, may prevent fish from returning. As well, fish of all kends require different habitats for feeding, resting, rearing, and spawning through the year. Preventing movement from one habitat to another can cause mortality. Permits for work in and around water are required for all in-stream work. Note: many stream-side activities may also require permits too. As with any permitting requirements, lead time is neded to avoid delays.

Construction Practices

Many processes can be implemented to protect fish habitat during construction. First and foremost is to time your project to correspond with "working windows" when fish are less likely to be impacted. Some methods of mitigating impact during construction include using erosion and sediment control measures to minimize stream sedimentation or instream work and, where it is recognized that instream work is unavoidable, isolate the worksite, and provide fish passage and protection during and after construction. Riparian areas must be protected to preserve the stream bank and ecosystem integrity.

Sediment from road and construction area runoff may be controlled through soil filtering and containment systems such as filter cloths and hay bales, settling bains, sediment booms, silt fences, and adjacent naturally vegetated areas. Deleterios substances such as lubricating or hydraulic oil, uncured concrete, wood preservatives, paints, explosives, and fuels must be contained to ensure that they do not enter streams.

From modification or construction activities, all areas of exposed soil must be revegetated within the first frowing season by hand or hydro-seeding and, if needed, planted with riparian vegetation. Vegetation must be maintained until the area is stabilized and natural vegetation is re-established.

Riparian management areas

Riparian Management Areas are areas immediately adjacent to streams, lakes, and wetlands. While these areas can vary considerably in appearance, size and presence of fish, they are characterized by their proximity to water. Because of this proximity, the vegetative cover in reiparian areas is generally distinctive and varies from the drier uplands to the moister lowland areas. These areas are usually more complex in terms of biological diversity than the surrounding upland areas. It is also important to be aware that the effects of ativities in the upper reaches or headwaters of a system can impact the values of downsream areas.

Stream Crossings Directory
Introduction Crossing Structures
Planning Revegetation
Protecting Aquatic Habitat Deactivation
Information for this wall chart was compiled by Eric L. Kay, of  Kay and Associates, Forest Road Consultants and International Training Consultants

This wall chart was produced by Logging and Sawmilling Journal