diff --git a/account_manager/src/validator/create.rs b/account_manager/src/validator/create.rs
index bbd2cbc99..da0112105 100644
--- a/account_manager/src/validator/create.rs
+++ b/account_manager/src/validator/create.rs
@@ -114,7 +114,7 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
 
 pub fn cli_run<T: EthSpec>(
     matches: &ArgMatches,
-    mut env: Environment<T>,
+    env: Environment<T>,
     validator_dir: PathBuf,
 ) -> Result<(), String> {
     let spec = env.core_context().eth2_config.spec;
diff --git a/beacon_node/genesis/tests/tests.rs b/beacon_node/genesis/tests/tests.rs
index 58f28702b..aaf6a7bea 100644
--- a/beacon_node/genesis/tests/tests.rs
+++ b/beacon_node/genesis/tests/tests.rs
@@ -24,7 +24,7 @@ pub fn new_env() -> Environment<MinimalEthSpec> {
 
 #[test]
 fn basic() {
-    let mut env = new_env();
+    let env = new_env();
     let log = env.core_context().log().clone();
     let mut spec = env.eth2_config().spec.clone();
 
diff --git a/database_manager/src/lib.rs b/database_manager/src/lib.rs
index 5d0c12b5f..33accfc05 100644
--- a/database_manager/src/lib.rs
+++ b/database_manager/src/lib.rs
@@ -288,7 +288,7 @@ pub fn prune_payloads<E: EthSpec>(
 }
 
 /// Run the database manager, returning an error string if the operation did not succeed.
-pub fn run<T: EthSpec>(cli_args: &ArgMatches<'_>, mut env: Environment<T>) -> Result<(), String> {
+pub fn run<T: EthSpec>(cli_args: &ArgMatches<'_>, env: Environment<T>) -> Result<(), String> {
     let client_config = parse_client_config(cli_args, &env)?;
     let context = env.core_context();
     let log = context.log().clone();
diff --git a/lcli/src/block_root.rs b/lcli/src/block_root.rs
index 7631872c5..a47b48a30 100644
--- a/lcli/src/block_root.rs
+++ b/lcli/src/block_root.rs
@@ -37,7 +37,7 @@ use types::{EthSpec, FullPayload, SignedBeaconBlock};
 
 const HTTP_TIMEOUT: Duration = Duration::from_secs(5);
 
-pub fn run<T: EthSpec>(mut env: Environment<T>, matches: &ArgMatches) -> Result<(), String> {
+pub fn run<T: EthSpec>(env: Environment<T>, matches: &ArgMatches) -> Result<(), String> {
     let spec = &T::default_spec();
     let executor = env.core_context().executor;
 
diff --git a/lcli/src/eth1_genesis.rs b/lcli/src/eth1_genesis.rs
index 80bcff909..34144cd86 100644
--- a/lcli/src/eth1_genesis.rs
+++ b/lcli/src/eth1_genesis.rs
@@ -13,7 +13,7 @@ use types::EthSpec;
 pub const ETH1_GENESIS_UPDATE_INTERVAL: Duration = Duration::from_millis(7_000);
 
 pub fn run<T: EthSpec>(
-    mut env: Environment<T>,
+    env: Environment<T>,
     testnet_dir: PathBuf,
     matches: &ArgMatches<'_>,
 ) -> Result<(), String> {
diff --git a/lcli/src/skip_slots.rs b/lcli/src/skip_slots.rs
index 8bd9af99a..49d1dd424 100644
--- a/lcli/src/skip_slots.rs
+++ b/lcli/src/skip_slots.rs
@@ -59,7 +59,7 @@ use types::{BeaconState, CloneConfig, EthSpec, Hash256};
 
 const HTTP_TIMEOUT: Duration = Duration::from_secs(10);
 
-pub fn run<T: EthSpec>(mut env: Environment<T>, matches: &ArgMatches) -> Result<(), String> {
+pub fn run<T: EthSpec>(env: Environment<T>, matches: &ArgMatches) -> Result<(), String> {
     let spec = &T::default_spec();
     let executor = env.core_context().executor;
 
diff --git a/lcli/src/transition_blocks.rs b/lcli/src/transition_blocks.rs
index b25cec81b..84d0a5176 100644
--- a/lcli/src/transition_blocks.rs
+++ b/lcli/src/transition_blocks.rs
@@ -94,7 +94,7 @@ struct Config {
     exclude_post_block_thc: bool,
 }
 
-pub fn run<T: EthSpec>(mut env: Environment<T>, matches: &ArgMatches) -> Result<(), String> {
+pub fn run<T: EthSpec>(env: Environment<T>, matches: &ArgMatches) -> Result<(), String> {
     let spec = &T::default_spec();
     let executor = env.core_context().executor;
 
diff --git a/lighthouse/environment/src/lib.rs b/lighthouse/environment/src/lib.rs
index 49163b96f..c5b58581d 100644
--- a/lighthouse/environment/src/lib.rs
+++ b/lighthouse/environment/src/lib.rs
@@ -380,7 +380,7 @@ impl<E: EthSpec> Environment<E> {
     }
 
     /// Returns a `Context` where no "service" has been added to the logger output.
-    pub fn core_context(&mut self) -> RuntimeContext<E> {
+    pub fn core_context(&self) -> RuntimeContext<E> {
         RuntimeContext {
             executor: TaskExecutor::new(
                 Arc::downgrade(self.runtime()),
@@ -395,7 +395,7 @@ impl<E: EthSpec> Environment<E> {
     }
 
     /// Returns a `Context` where the `service_name` is added to the logger output.
-    pub fn service_context(&mut self, service_name: String) -> RuntimeContext<E> {
+    pub fn service_context(&self, service_name: String) -> RuntimeContext<E> {
         RuntimeContext {
             executor: TaskExecutor::new(
                 Arc::downgrade(self.runtime()),