--- title: "EPA Aquatic Life Limits: Dissolved Oxygen, pH | Aethair" description: "EPA Ambient Water Quality Criteria (Aquatic Life) limit values for Dissolved Oxygen and pH: every value and averaging period, who the standard applies to,…" url: https://aethair.io/standards/epa_aquatic_life/ --- Compliance · US EPA (Clean Water Act) # EPA Ambient Water Quality Criteria (Aquatic Life) Surface water: aquatic-life protection, USA The Ambient Water Quality Criteria for the protection of aquatic life are the pollutant concentrations and physical-chemical conditions that the US Environmental Protection Agency (EPA) recommends surface waters should meet to keep aquatic ecosystems healthy. Developed under the Clean Water Act, they cover conventional parameters such as **dissolved oxygen, pH, and temperature**, together with nutrients, ammonia, and a long list of toxic substances. Many toxic criteria are expressed as two values: an **acute** (criterion maximum) concentration protecting against short exposures and a **chronic** (criterion continuous) concentration protecting against prolonged exposure. [Schedule a call](https://calendly.com/d/ctdd-mkr-v9v/aethair-demo-website) [Configure EPA aquatic life Monitoring](https://aethair.io/build/?params=do,ph) At a glance **US EPA (Clean Water Act)** Surface water: aquatic-life protection, USA 2 parameters · 2 limit values [Dissolved Oxygen](https://aethair.io/parameters/do/) [pH](https://aethair.io/parameters/ph/) 1 device measures them all - **Thiamis** YSI Water Quality Sondes [Official text from US EPA (Clean Water Act)](https://www.epa.gov/wqc) The standard ## What the EPA Aquatic Life Criteria Are The criteria are scientific recommendations rather than direct regulations; states and tribes adopt them, often with local modification, into their enforceable water-quality standards. The parameters and their criteria are given in the limit table on this page. Limit values ## EPA aquatic life Limit Values Every value US EPA (Clean Water Act) publishes for the 2 parameters below, with its averaging period, as the standard states it. [**Dissolved Oxygen** Water Quality](https://aethair.io/parameters/do/) **5 mg/L** *1-day minimum (warmwater, early life stages)* 3 mg/L for other life stages; the coldwater criteria are higher (EPA 1986 DO criteria) [**pH** Water Quality](https://aethair.io/parameters/ph/) **6.5–9 pH** *Acceptable range* Who it applies to ## Who Uses It State and tribal environmental agencies use the criteria as the scientific basis for their surface-water standards, which in turn govern discharge permits, impaired-water listings, and cleanup plans. Industrial and municipal dischargers must keep their effluent within the resulting limits, and consultants, researchers, and watershed groups measure rivers, lakes, and estuaries against the criteria to judge ecological health. Anyone assessing whether a water body can support fish and other aquatic organisms (regulators, permit holders, and scientists alike) works from these values. Monitoring ## How Monitoring Demonstrates Compliance The core aquatic-life parameters (dissolved oxygen, pH, temperature, and conductivity) are exactly those a **multiparameter water-quality sonde** measures continuously in situ. Dissolved oxygen is often the decisive one, because it swings over a day-and-night cycle and can crash below the criterion during warm, low-flow conditions that a single daytime grab sample would miss. A sonde on a Thiamis gateway captures these diurnal patterns and short-lived excursions against the values in the limit table on this page, while toxic pollutants such as metals, ammonia, and pesticides are quantified by laboratory analysis of collected samples. Continuous monitoring reveals when and why conditions breach a criterion; laboratory work supplies the definitive figures for the substances a sonde cannot measure. [Customize this configuration](https://aethair.io/build/?params=do,ph) ### Who measures each parameter | Parameter | Aethair PRO | Aethair IAQ | External | | - | - | - | - | | [Dissolved Oxygen](https://aethair.io/parameters/do/) | — | — | [5 instruments](https://aethair.io/parameters/do/) via Thiamis | | [pH](https://aethair.io/parameters/ph/) | — | — | [5 instruments](https://aethair.io/parameters/ph/) via Thiamis | Devices ## Devices That Cover EPA aquatic life How much of this standard one Aethair monitor covers, followed by the third-party instruments in the sensor catalog that measure its parameters. Each connects to Environet through a Thiamis gateway, which adds whatever the monitor leaves out. Covers both on its own [**YSI EXO** Water Quality Sondes](https://aethair.io/sensors/ysi-water-quality-sondes/) [**In-Situ** Water Quality Sondes](https://aethair.io/sensors/in-situ-water-quality-sondes/) [**Eureka Water Probes Manta2** Water Quality Sondes](https://aethair.io/sensors/eureka-water-probes-water-quality-sondes/) [**Spectra Scientific Spectra Litmus** Water Quality Sondes](https://aethair.io/sensors/spectra-scientific-water-quality-sondes/) [**YSI** Water Quality Sondes](https://aethair.io/sensors/ysi-water-quality-sondes/) Solutions ## Solutions Judged Against EPA aquatic life ### [Aquaculture & Fish Farming](https://aethair.io/solutions/aquaculture/) Dissolved oxygen, temperature, and ammonia control ### [Water Quality Monitoring](https://aethair.io/solutions/water-quality/) Rivers, lakes, drinking water, and stormwater [All solutions](https://aethair.io/solutions/) Questions ## EPA aquatic life FAQ What is the difference between acute and chronic criteria? Acute criteria set the highest concentration a water body may briefly reach without harming aquatic life, while chronic criteria set a lower concentration safe for prolonged exposure. Expressing a pollutant as both recognizes that a short spike and a sustained level cause harm in different ways. Are the aquatic life criteria legally binding? Not directly. They are EPA scientific recommendations; states and tribes adopt them, sometimes adjusted for local conditions, into their own enforceable water-quality standards. It is those adopted standards, rather than the federal criteria themselves, that carry legal force. Why is dissolved oxygen so important for aquatic life? Fish and aquatic invertebrates need dissolved oxygen to breathe, and it is the parameter most likely to fall to lethal levels, depleted by warm temperatures, organic pollution, and respiration at night. Because it varies so much over a day, continuous measurement is far more revealing than an occasional sample. How do I monitor surface water for aquatic-life criteria? Use a multiparameter sonde on a Thiamis gateway measuring dissolved oxygen, pH, temperature, and conductivity continuously, supplemented by laboratory analysis for toxic substances. Use the configurator to set up the sonde for river, lake, or estuary deployment.